AO Smith Water Heater HWB 399 User Guide
MODELS HW/HWB 300, 399, 420, 520, 610, 670  
GAS-FIRED COMMERCIAL COPPER BOILERS FOR  
HYDRONIC HEATINGAND HOT WATER SUPPLY  
UP-FLOW MODELS  
• INSTALLATION • OPERATION • MAINTENANCE • LIMITED WARRANTY  
• INDOOR ONLY  
WARNING: If the information in this manual  
is not followed exactly, a fire or explosion  
may result causing property damage,  
personal injury or death.  
— Do not store or use gasoline or other  
flammable vapors and liquids in the  
vicinity of this or any other appliance.  
— WHAT TO DO IF YOU SMELL GAS  
• Do not try to light any appliance.  
• Do not touch any electrical switch;  
CAUTION  
do not use any phone in your  
TEXT PRINTED OR OUTLINED IN RED CONTAINS INFORMATION  
building.  
RELATIVE TO YOUR SAFETY. PLEASE READ THOROUGHLY  
BEFORE USING APPLIANCE.  
• Immediately call your gas supplier  
from a neighbor's phone. Follow the  
gas supplier's instructions.  
• If you cannot reach your gas supplier,  
call the fire department.  
— Installation and service must be  
performed by a qualified installer,  
service agency or the gas supplier.  
ADIVISION OFA.O. SMITH CORPORATION  
MC BEE, SC SEATTLE, WA  
STRATFORD, ONTARIO  
VELDHOVEN, THE NETHERLANDS  
www.hotwater.com  
PLACE THESE INSTRUCTIONS ADJACENT TO BOILER AND  
NOTIFY OWNER TO KEEP FOR FUTURE REFERENCE  
PART NO. 211683-000 REV.02  
SUPERSEDES PART NO'S, 210288-000 REV. 01 & 192356-000  
PRINTED IN U.S.A. 0905  
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ROUGH-IN DIMENSIONS  
EXTRA OPENING  
FOR THERMOMETER  
AND RELIEF VALVE  
HW/HWB-520, 610  
AND HW--670  
HW/HWB-610  
AND HW-670  
NATURAL GAS ONLY  
TABLE 1  
MODELS  
Prop.  
HWB/  
Nat.  
HWB/  
HWB/  
HW-300  
65 (1651)  
HWB/  
HW-399  
HWB/  
HW-420  
HWB/  
HW-520  
DIMENSIONS IN INCHES  
HW-610/670 HW-610/670  
57-1/8 (1451) 57-1/8 (1451) 68-5/16 (1735) 67 (1702) 64-3/4 (1645)  
43-1/4 (1099) 45-1/8 (1146) 45-1/8 (1146) 56-1/4 (1429) 56-1/4 (1429) 56-1/4 (1429)  
A
B
C
D
E
F
G
H
J
Overall height  
Height to top of jacket  
Floor to center line water inlet  
Diameter of jacket  
Floor to center line water outlet  
Draft diverter outlet diameter  
Floor to center line gas inlet  
Overall depth  
36 (914)  
25-1/4 (641)  
12 (305)  
8 (203)  
16-1/2 (419)  
29-5/8 (753)  
9 (229)  
38-3/4 (984)  
27 (686)  
12 (305)  
10 (254)  
16-3/4 (425)  
31-1/2 (800)  
9 (229)  
38-3/4 (984)  
27 (686)  
12 (305)  
10 (254)  
16-3/4 (425)  
31-1/2 (800)  
9 (229)  
46 (1168)  
27 (686)  
12 (305)  
10 (254)  
18 (457)  
46 (1168)  
27 (686)  
12 (305)  
12 (305)  
18 (457)  
46 (1168)  
27 (686)  
12 (305)  
12 (305)  
18 (457)  
36-1/2 (927) 36-1/2 (927) 36-1/2 (927)  
Support height  
9(229)  
9 (229)  
9 (229)  
K
L
Width of control string (approx.)  
Pipe size of water inlet (NPT)  
Pipe size of water outlet(NPT)  
Pipe size of gas inlet (NPT)  
Control string plus 1/2 jacket dia. (approx.)  
Water outlet to jacket  
Water inlet casting to center line of jacket  
Horizontal length between water inlet and outlet 5-3/8 (137)  
Control string from jacket  
14 (356)  
1-1/4  
1-1/4  
3/4  
26-5/8 (676)  
1 (25)  
14 (356)  
1-1/2  
1-1/2  
14 (356)  
1-1/2  
1-1/2  
11(279)  
11 (279)  
11 (279)  
2
2
1
2
2
1
2
2
1
M
N
P
Q
R
S
T
1
1
27-1/2(699)  
1 (25)  
11-1/4 (286)  
5-1/2 (140)  
5 (127)  
27-1/2 (699)  
1 (25)  
11-1/4 (286)  
5-1/2 (140)  
5 (127)  
24-1/2 (622) 24-1/2 (622) 24-1/2 (622)  
3-1/2 (89)  
12 (305)  
5-3/4 (146)  
7 (178)  
3-1/2 (89)  
12 (305)  
5-3/4 (146) 5-3/4 (146)  
3-1/2 (89)  
12 (305)  
10-1/8 (257)  
5 (127)  
7 (178)  
7 (178)  
Approx. shipping weight lbs. (Kilograms)  
240 (109)  
291 (132)  
291 (132)  
361 (164)  
361 (164)  
361 (164)  
NOTE: All dimensions in inches (millimeters) except pipe size which is NPT.  
TABLE 2, SPECIFICATIONS - CANADIAN MODELS ONLY  
Maximum  
Maximum  
BTUH(KW)  
I.A.S.  
BTUH(KW)  
Maximum  
Heat Loss Load  
210,120 (62)  
274,371 (80)  
292,740 (86)  
364,650 (107)  
427,210 (125)  
414,800 (121)  
Max. Heat Transfer  
Surface Area (Sq. Ft.) Surface Area (Sq. Ft.)  
Max. Heat Transfer  
Model  
Type of Gas  
Natural & Propane  
Natural & Propane  
Natural & Propane  
Natural & Propane  
Natural  
HWB-300  
HWB-399  
HWB-420  
HWB-520  
HWB-610  
HWB-610  
300,000 (88)  
399,000 (116)  
420,000 (123)  
520,000 (152)  
610,000 (179)  
610,000 (179)  
247,200 (72)  
322,790 (95)  
344,400 (101)  
429,000 (126)  
502,600 (147)  
488,000 (143)  
1,410 (.41)  
1,829 (.54)  
1.952 (57)  
2,431 (.71)  
2,848 (.83)  
2,765 (.81)  
1,051 (.31)  
1,372 (.40)  
1,464 (.43)  
1,823 (.53)  
2,136 (.61)  
2,074 (.61)  
Propane  
Ratings shown are for current modern heating system design. Where A.O. Smith boilers are connected to heavy, cast iron radiator systems or where unusual pick-up or  
large size piping conditions exist, reduce ratings by 10%.  
NOTE: To compensate for the effects of high altitude areas above 2000 feet, the input, output and heating load ratings should be reduced  
approximately 4% for each 1000 feet above sea level.  
2
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TABLE 3, RECOVERY CAPACITIES - CANADIAN MODELS ONLY  
Input  
Temp. (C)  
11  
20  
17  
30  
22  
40  
26  
50  
33  
60  
39  
70  
44  
80  
50  
90  
56  
100  
1,001 1,001  
291 264  
1,464 1,331 1,220 1,127 1,046  
387 352 322 298 276  
1,542 1,401 1,285 1,186 1,101  
407 370 339 313 291  
1,909 1,735 1,590 1,468 1,363  
504 458 420 388 360  
2,239 2,035 1,866 1,722 1,599  
592 538 493 455 423  
61  
110  
67  
72  
78  
Model (Btu/Hr.) Rise (F)  
120  
918  
242  
130  
847  
224  
140  
786  
208  
HW-300 300,000  
HW-399 399,000  
HW-420 420,000  
HW-520 520,000  
HW-610 610,000  
LPH  
GPH  
LPH  
GPH  
LPH  
GPH  
LPH  
GPH  
LPH  
GPH  
5,505 3,670 2,753  
1,455 970 727  
7,322 4,882 3,661  
1,935 1,290 967  
7,708 5,138 3,854  
2,036 1,358 1,018  
9,543 6,362 4,771  
2,521 1,681 1,261  
11,194 7,463 5,597  
2,958 1,972 1,479  
2,202 1,835 1,573 1,376 1,223  
582 485 416 364 323  
2,929 2,441 2,092 1,831 1,627  
774 645 553 484 430  
3,083 2,569 2,202 1,927 1,713  
815 679 582 509 453  
3,817 3,181 2,727 2,386 2,121  
1,008 840 720 630 560  
4,478 3,731 3,198 2,799 2,488  
1,183 986 845 739 657  
3
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FOREWORD  
the locations indicated in the diagrams as these are necessary for checking  
the operation of the boiler.  
CAUTION  
TEXTPRINTEDOROUTLINEDINREDCONTAINSINFORMATIONRELATIVE  
TO YOUR SAFETY. PLEASE READ THOROUGHLY BEFORE USING MAKE SURETHE GAS ON WHICH THE BOILER WILLOPERATE IS THE  
SAMEASTHATSPECIFIEDONTHEUNITRATINGPLATE.  
APPLIANCE.  
The boiler installation must conform to these instructions and the  
Detailed installation diagrams are in this manual. These diagrams will serve  
to provide the installer with a reference for the materials and method of requirements of the local authority having jurisdiction.  
piping suggested. ITIS NECESSARYTHATALLWATERAND GAS PIPING  
Where required by authority having jurisdiction, the installation must conform  
to the Standard for Controls and Safety Devices for Automatically Fired  
Boilers, ANSI/ASME CSD-1.  
AND THE ELECTRICALWIRING BE INSTALLEDAND CONNECTEDAS  
SHOWNINTHEDIAGRAMS.  
CHECKTHEDIAGRAMSTHOROUGHLYBEFORESTARTINGINSTALLATION  
TOAVOID POSSIBLE ERRORSANDTO MINIMIZETIMEAND MATERIALS  
COST.  
In absence of local code requirements, the boiler installation must conform  
to the National Fuel Gas Code, ANSI Z223.1 and/or CAN/CSA B-149.1-00  
Installation Codes.  
This design complies with the latest edition of ANSI Z21.13.  
CSA4.9 low-pressure boiler.  
These manuals can be purchased from the CSA International, 8501 East  
Pleasant Valley Road, Cleveland, OH 44131 or 178 Rexdale Boulevard,  
Toronto, Ontario Canada M9W1R3.  
Particular attention should be given to the installation of thermometers at  
TABLE OF CONTENTS  
PAGE  
PAGE  
START-UPAND OPERATING INSTRUCTIONS .................................. 45  
Filling And Venting ...................................................................... 46  
Pilot and Main Burner ................................................................. 46  
Lighting Instructions ................................................................... 47-48  
Pilot and Main Burner (Continued) ............................................. 49-51  
Electronic Intermittent Pilot Ignition Control ................................. 51  
Normal Operating Sequence With Honeywell S-8600H or  
ROUGH-INDIMENSIONS ................................................................... 2-3  
FOREWORD ......................................................................................  
INSTALLATION INSTRUCTIONS ........................................................  
Required Ability ..........................................................................  
Installation As Boiler Replacement .............................................  
Location ......................................................................................  
4
4
4
4
5
Air Requirements ........................................................................ 5-6  
S-8610M Intermittent Ignition Control (I.I.D.) ............................... 52  
High Altitude Installations ........................................................... 52  
Thermal Balancer ....................................................................... 52  
Coil High Limit Control (Protector Switch) .................................. 52-53  
Pressure Reducing Valve .......................................................... 53  
Safety Flow Switch ................................................................... 53-54  
Safety Relief Valve Maintenance ............................................... 54  
Chemical Vapor Corrosion .........................................................  
Installation Clearances ...............................................................  
Levelling ......................................................................................  
6
6
6
System Connections .................................................................. 6-9  
Gas Connections ........................................................................ 9-11  
Gas Pressure Regulators .......................................................... 11-12  
Venting The Boiler - Standard Venting....................................... 12-14  
Replacement Parts .....................................................................  
REMOVAL OF EXISTING BOILER FROMACOMMON  
54  
Venting Maintenance - Standard Venting ..................................  
Venting Sidewall (Optional) Power Vent System ...................... 15  
Venting System .......................................................................... 15  
15  
VENTING SYSTEM ............................................................................ 54  
GENERAL MAINTENANCE ................................................................ 55  
Relief Valve ................................................................................  
55  
Safety Relief Valves .................................................................. 15-16  
Wiring Connections .................................................................... 16-31  
CLEANING AND FLUSHING INSTRUCTIONS .................................... 55  
Internal Contaminants ................................................................. 55  
Hot Water Supply Boilers - Preventive Maintenance ................ 55  
Deliming ....................................................................................... 55-56  
Deliming Solvents ....................................................................... 56  
Heavy Lime Deposits ................................................................. 56  
Removing Silicate ....................................................................... 56  
Water Line Connections .............................................................  
Hard Water .................................................................................  
32  
32  
Tank Temperature Control .......................................................... 32-33  
Low Water Cutoff ...................................................................... 33  
Thermometers ............................................................................ 33  
Drain Valve (Not Supplied) .........................................................  
33  
PRE-TROUBLE-SHOOTING ...............................................................  
57  
Closed Water System ................................................................ 33  
TROUBLE-SHOOTING ....................................................................... 57-61  
Piping Diagrams .......................................................................... 34-45 LIMITED WARRANTY ........................................................................ 62  
INSTALLATION INSTRUCTIONS  
REQUIRED ABILITY  
With old systems where water temperature can be expected to  
drop appreciably due to long standby periods, a bypass pipe of at  
least 1" size with a balancing cock should be installed between  
the boiler inlet and outlet. When the system first starts, the valve  
should be slowly opened until the condensing ceases. This  
adjustment remains at a permanent setting to establish required  
temperature rise across the boiler.  
INSTALLATION OR SERVICE OFTHIS BOILER REQUIRESABILITY  
EQUIVALENT TO THAT OF A LICENSED TRADESMAN IN THE  
FIELD INVOLVED. PLUMBING, AIR SUPPLY, VENTING, GAS  
SUPPLY AND ELECTRICAL WORK ARE REQUIRED.  
INSTALLATIONAS BOILER REPLACEMENT  
Installation as boiler replacement on an old system with large  
water volume may experience condensation within the boiler on  
cold starts. This condensing of water vapor in the combustion  
area can be prevented if a portion of the system water flow is  
diverted past the boiler to cause an increase in boiler temperature  
rise.  
The equipment shall be installed in accordance with those  
installation regulations in force in the local area where the  
installation is to be made. These shall be carefully followed in all  
cases. Authorities having jurisdiction shall be consulted before  
installations are made.  
4
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LOCATION  
WARNING  
FOR SAFE OPERATION PROVIDE ADEQUATE AIR FOR  
COMBUSTION AND VENTILATION. AN INSUFFICIENT SUPPLY  
OF AIR WILL CAUSE RECIRCULATION OF COMBUSTION  
PRODUCTS RESULTING INAIR CONTAMINATION THAT MAY BE  
HAZARDOUS TO LIFE. SUCH A CONDITION OFTEN WILL  
RESULT IN A YELLOW, LUMINOUS BURNER FLAME, CAUSING  
CARBONING OR SOOTING OF THE COMBUSTION CHAMBER,  
BURNERS AND FLUE TUBES AND CREATES A RISK OF  
ASPHYXIATION.  
When installing the boiler, consideration must be given to proper  
location. Location selected should be as close to the stack or  
chimney as practicable with adequate air supply and as centralized  
with the piping system as possible. This location should also be  
such that the gas ignition system components are protected from  
water (dripping, spraying, etc.) during appliance operation and  
service (circulator replacement, control replacement, etc.).  
THE BOILER MUST NOT BE INSTALLED ON CARPETING.  
UNCONFINEDSPACE  
THE BOILER SHOULD NOT BE LOCATED INANAREAWHERE IT  
WILL BE SUBJECT TO FREEZING.  
In buildings of conventional frame, brick or stone construction,  
unconfined spaces may provide adequate air for combustion, and  
draft hood dilution.  
LOCATE IT NEAR A FLOOR DRAIN. THE BOILER SHOULD BE  
LOCATED INANAREAWHERE LEAKAGE FROM THE BOILER OR  
CONNECTIONS WILL NOT RESULT IN DAMAGE TO THE  
ADJACENT AREA OR TO LOWER FLOORS OF THE STRUCTURE.  
If the unconfined space is within a building of tight construction  
(buildings using the following construction: weather stripping, heavy  
insulation, caulking, vapor barrier, etc.) air for combustion,  
ventilation, and draft hood dilution must be obtained from outdoors  
or spaces freely communicating with the outdoors. The installation  
instructions for confined spaces in tightly constructed buildings  
must be followed to ensure adequate air supply.  
WHEN SUCH LOCATIONS CANNOT BE AVOIDED, A SUITABLE  
DRAIN PAN SHOULD BE INSTALLED UNDER THE BOILER. Such  
pans should be fabricated with sides at least 60mm (2-1/2") deep,  
with length and width at least 50mm (2") greater than the diameter  
of the boiler and must be piped to an adequate drain. The pan  
must not restrict combustion air flow.  
CONFINEDSPACE  
(a) U. S. INSTALLATIONS  
WARNING  
KEEPING BOILER AREA CLEAR AND FREE FROM COMBUSTIBLE  
MATERIALS, GASOLINEAND OTHER FLAMMABLE VAPORSAND  
LIQUIDS.  
When drawing combustion and dilution air from inside a  
conventionally constructed building to a confined space, such a  
space shall be provided with two permanent openings, ONE  
WITHIN 12 INCHES OF THE ENCLOSURE TOP AND ONE  
WITHIN 12 INCHES OF THE ENCLOSURE BOTTOM. Each  
opening shall have a free area of at least one square inch per  
1000 Btuh of the total input of all appliances in the enclosure, but  
not less than 100 square inches.  
WARNING  
THERE IS A RISK IN USING FUEL BURNING APPLIANCES SUCH  
AS BOILERS IN ROOMS OR AREAS WHERE GASOLINE, OTHER  
FLAMMABLE LIQUIDS OR ENGINE DRIVEN EQUIPMENT OR  
VEHICLES ARE STORED, OPERATED OR REPAIRED.  
FLAMMABLE VAPORS ARE HEAVY AND TRAVEL ALONG THE  
FLOORAND MAY BE IGNITED BYTHE IGNITER OR MAIN BURNER  
FLAMES CAUSING FIRE OR EXPLOSION. SOME LOCAL CODES  
PERMIT OPERATION OF GAS APPLIANCES IF INSTALLED  
18 INCHES OR MORE ABOVE THE FLOOR. THIS MAY REDUCE  
THE RISK IF LOCATION IN SUCHANAREACANNOT BEAVOIDED.  
If the confined space is within a building of tight construction, air  
for combustion, ventilation, and draft hood dilution must be  
obtained from outdoors. When directly communicating with the  
outdoors or communicating with the outdoors through vertical  
ducts, two permanent openings, located in the above manner,  
shall be provided. Each opening shall have a free area of not less  
than one square inch per 4000 Btuh of the total input of all  
appliances in the enclosure. If horizontal ducts are used, each  
opening shall have a free area of not less than one square inch  
per 2000 Btuh of the total input of all appliances in the enclosure.  
WARNING  
FLAMMABLE ITEMS, PRESSURIZED CONTAINERS OR ANY  
OTHER POTENTIAL FIRE HAZARDOUS ARTICLES MUST NEVER  
BE PLACED ON OR ADJACENT TO THE BOILER. OPEN  
CONTAINERS OF FLAMMABLE MATERIALMUSTNOT BE STORED  
OR USED IN THE SAME ROOM WITH THE BOILER.  
(b) CANADIAN INSTALLATIONS  
Ventilation of the space occupied by the boiler(s) shall be provided  
by an opening for ventilation air at the highest practical point  
communicating with outdoors. The total cross-sectional area shall  
be at least 10% of the area of the combustion air opening but in no  
case shall the cross-sectional area be less than 10 square inches  
(6500 mm2)  
A hot water boiler installed above radiation level or as required by  
the authority having jurisdiction, must be provided with a low water  
cutoff device at the time of boiler installation.  
In additional to the above, there shall be permanent air supply  
opening(s) having a cross-sectional area of not less than 1 square  
inch per 7,000 BTUH (310 mm2/KW) up to and including  
1,000,000 BTUH plus 1 square inch per 14,000 BTU in excess of  
1,000,000 BTUH. This opening(s) shall be located at, or ducted  
to, a point neither more than 18" (450 mm) nor less than 6 inches  
(150 mm) above the floor level.  
AIR REQUIREMENTS  
Provisions for combustion and ventilation air in accordance with  
section 5.3, Air for Combustion and Ventilation, of the National  
Fuel Gas Code, ANSI Z223.1, or sections 7.2, 7.3, or 7.4 of  
CAN/CSA B149.1-00, Installation Codes, or applicable provisions  
of the local building codes.  
Where power vented equipment is used in the same room as the  
boiler, sufficient air openings must be supplied.  
Provisions for vent, bleed and gas relief lines (when applicable).  
Keep appliance area free of combustible or flammable liquids.  
Do not obstruct the flow of combustion or ventilating air.  
UNDERSIZED OPENINGS MAY RESULT IN INSUFFICIENT AIR  
FOR COMBUSTION.  
5
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TABLE 4  
Where an exhaust fan is installed in the same room with a boiler,  
sufficient openings for air must be provided in the walls.  
HWB/HW HWB/HW HWB/HW  
HWB/HW HWB/HW  
520 610 & 670  
UNDERSIZED OPENINGS WILL CAUSE AIR TO BE DRAWN INTO  
THE ROOM THROUGH THE CHIMNEY, CAUSING POOR  
COMBUSTION. SOOTING MAY RESULT WITH AN INCREASED  
RISK OFASPHYXIATION.  
300  
399  
420  
TOP 28" (711.2) 32" (812.8) 24" (609.6) 24" (609.6) 24" (609.6)  
SIDES 6" (152.4) 6" (152.4) 24" (609.6) 24" (609.6) 24" (609.6)  
REAR 6" (152.4) 6" (152.4) 24" (609.6) 24" (609.6) 24" (609.6)  
VENT 6" (152.4) 6" (152.4) 6" (152.4) 6" (152.4) 6" (152.4)  
CHEMICALVAPOR CORROSION  
Two inch (50.8mm) clearance is allowable from combustible  
construction for hot water pipes.  
WARNING  
CORROSION OF THE FLUEWAYS AND VENT SYSTEM MAY  
OCCUR IF AIR FOR COMBUSTION CONTAINS CERTAIN  
CHEMICALVAPORS WHICH BREAK DOWN INTOACIDSAT HIGH  
TEMPERATURE. SUCH CORROSION MAY RESULT IN FAILURE  
AND RISK OFASPHYXIATION.  
Sufficient area should be provided at the front and rear of the unit  
for proper servicing. Clearances of 24 inches (609.4mm) in the  
rear and 48 inches (1,219mm) in the front are required by code. In  
a utility room installation, the door shall be wide enough to allow  
the boiler to enter or to permit the replacement of another appliance  
such as a water heater.  
Water boiler corrosion and component failure can be caused by  
the heating and breakdown of airborne chemical vapors. Spray  
can propellants, cleaning solvents, refrigerator and air conditioning  
refrigerants, swimming pool chemicals, calcium and sodium  
chloride, waxes, and process chemicals are typical compounds  
which are corrosive. These materials are corrosive at very low  
concentration levels with little or no odor to reveal their presence.  
Products of this sort must not be stored near the boiler. Also, air  
which is brought in contact with the water boiler should not contain  
any of these chemicals. If necessary, uncontaminated air should  
be obtained from remote or outside sources.  
LEVELLING  
Each unit should be checked after installation to be certain that it is  
level.  
If the unit is not level, insert metal shims under the legs of the unit  
to correct this condition.  
SYSTEM CONNECTIONS  
INSTALLATION CLEARANCES  
The system installation must conform to these instructions and to  
the requirements of the local code authority having jurisdiction.  
Good practice requires that all heavy piping be supported.  
These boilers are approved for installation on combustible flooring  
in an alcove with minimum clearance to combustibles of:  
ATYPICALBOILER INSTALLATION  
FIGURE1  
6
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1. CONVENTIONAL INSTALLATIONS  
All modern hydronic type boilers are exceptionally fast heating units.  
The low water volumes in relation to firing rates require special  
attention to water flow rates for smooth, efficient operation. These  
considerations for the A. O. Smith copper heat exchanger boilers  
are covered below.  
Conventional 100C (200F) drop in systems for a fully loaded boiler  
will maintain the following approximate flow rates:  
U.S.  
CANADIAN  
MODELS  
HWB-300  
HWB-399  
HWB-420  
HWB-520  
HWB-610  
MODELS  
HW-300  
HW-399  
HW-420  
HW-520  
HW-670  
LPM  
87  
GPM  
23  
114  
132  
148  
175  
30  
35  
39  
46  
Figure 1 shows a typical installation of the boiler with pipe sizing  
and circulator selected by the installer to provide adequate water  
flow whenever the boiler is firing.  
ONE BOILER INSTALLED  
INDEPENDENT OF THE PRIMARY SYSTEM  
FIGURE2  
In a system with several large zones of which any might be smaller  
than approximately 1/3 of the system should include a hydronic  
balancer as shown in fig. 1. The balancer connects between the  
system supply and the return line before the circulator inlet.  
Adjustment of the balancing cock should permit adequate boiler  
flow rate when only the smallest zone is in operation.  
Total heating requirements for the building can be supplied by a  
series of boiler loops all connecting to a common pipe joining the  
system supply and return mains. The supply and return branches  
of each boiler loop must join the common pipe only a short nipple  
length apart. The different sets of branches should be installed  
reasonably close together, but not necessarily to the short nipple  
length as required for the supply and return of each set. These  
branches may be made with tees or with welded connections.  
Attention should be given to balancing inputs and water flow rates  
where wide variations of system flow rates can occur.  
The recommended minimum flow rates that will result in  
approximately 300C (500F) temperature rise across the boiler are  
as follows:  
The installer is reminded that the total boiler flow rates need not  
match the system flow rate.  
TABLE 5  
PUMPAND PIPE SIZING DATA  
(PIPING FROM TEES IN MAIN TO BOILER BRANCHES)  
U.S.  
CANADIAN  
MODELS  
HWB-300  
HWB-399  
HWB-420  
HWB-520  
HWB-610  
MODELS  
HW-300  
HW-399  
HW-420  
HW-520  
HW-610  
HW-670  
LPM  
34  
45  
53  
61  
GPM  
9
12  
14  
16  
Quantity and Model  
Temp.  
Rise°C (°F) G.P.M.  
*Pump  
Size  
1-1/2"PR  
150  
125  
100  
60-13  
1-1/2"HV  
150  
Pipe  
Size  
2"  
1-1/2"  
1-1/4"  
1"  
U.S  
Canadian  
10 (20)  
15 (30)  
15 (30)  
20 (40)  
10 (20)  
15 (30)  
20 (40)  
20 (40)  
10 (20)  
15 (30)  
20 (40)  
20 (40)  
10 (20)  
10 (20)  
17 (35)  
20 (40)  
10 (20)  
15 (30)  
17 (35)  
20 (40)  
23  
15  
15  
11  
30  
20  
15  
15  
32  
21  
16  
16  
39  
26  
23  
20  
51  
34  
29  
25  
69  
76  
18  
20  
HW-300  
1 HWB-300  
If system flow rate is unknown, or if zoning creates extreme  
variations in flow rates, the boiler should be installed as shown  
in fig. 2 for A. O. Smith LINEAR-TEMP installations.  
2"  
HW-399  
HW-420  
HW-520  
HW-670  
1 HWB-399  
1 HWB-420  
1 HWB-520  
1 HWB-610  
1-1/2"  
1-1/2"  
1-1/4"  
2"  
1-1/2"  
1-1/2"  
1-1/4"  
2-1/2"  
2"  
1-1/2"  
1-1/2"  
3"  
2-1/2"  
2"  
125  
60-13  
1-1/2"HV  
150  
2. LINEAR-TEMPINSTALLATIONS  
A. New Installations  
125  
2-1/2"  
1-1/2"HV  
1-1/2"HV  
150  
60-13  
2-1/2"  
2"  
A. O. Smith LINEAR-TEMP systems have been designed to provide  
efficient, trouble-free operation of the boiler sizes covered in this  
manual with any of the following conditions:  
a. Unknown system flow rate  
b. Varying flow rate as with zoned systems  
c. Multiple boiler installations  
1-1/2"HV  
1-1/2"  
Figure 2 shows piping and accessory arrangement for a boiler  
pumped independent of the primary system mains. Pipe sizing  
and boiler loop pump selection data are shown in Table 5 for  
several different temperature rises across the boilers.  
NOTE: Pipe loop sizes and pump selections based on  
50 equivalent feet of pipe and fittings.  
*All pump sizes listed are B & G model numbers.  
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NO.  
1
SUGGESTED ITEMS FOR INSTALLATION  
Short pipe nipple and pair of boiler loop tees in piping  
between system supply and return. One set per each  
group of boilers  
2
3
4
5
6
7
Boiler pipe loop. See piping sizing data above.  
Boiler circulator. See pump sizing data above.  
Thermometer.  
Theraltimeter.  
Plug cock to control flow rate.  
Safety flow switches. For interlock with other systems or  
instead of low water cutoff.  
8
9
Relief valve.  
With one -300, -399 or -420 item 9 is - sensing  
element of remote control.  
With a group of -300's, -399's or -420's, item 9 is - for  
1st. boiler, the sensing element as above. For additional  
boilers, install a 2nd. limit control if required by local codes.  
With any -520, -610 or 670 boilers, install 2nd. limit control  
here if required by local code.  
SCHEMATIC OF THE LINEAR-TEMP® SYSTEM  
FIGURE3  
BOILER INLET - OUTLET SIZES  
10 HWB-300 - 1-1/4", HWB-399 - 1-1/2", HWB-420-1-1/2",  
HWB-520 & HWB-610 - 2". Canadian Models  
10 HW-300 - 1-1/4", HW-399 - 1-1/2", HW-420-1-1/2",  
HW-520 & HW-670 - 2". U.S. Models  
Supply and return headers of the old system should be connected  
to the boiler loop with a pair of tees set close together. The boiler  
loop pump and the boiler(s) should be wired to operate only when  
any of the system pumps are in operation. The number of zone  
pumps that may be in operation at any particular time will take their  
required flow rate out from the first tee in the boiler piping. This  
water will be circulated through the proper branches from the supply  
header to the zones calling for heat. The water will be brought  
back to the return header and then into the second tee in the boiler  
pipe loop. There will be no conflict between the boiler pump and  
the zone pumps when the two tees in the boiler loop are placed  
close together.  
MINIMUM BRANCH SIZES TO BOILERS  
11 HWB-300 - 1-1/4"  
HWB-399 - 1-1/2"  
HWB-420 - 1-1/2"  
11 HW-300 - 1-1/4"  
HW-399 - 1-1/2"  
HWB-520, 610 (Single boiler  
per pump) 2"  
Canadian Models  
HW-520, 670 (Single boiler  
per pump) 2"  
HW-420 - 1-1/2"  
U.S. Models  
12 Flow control valve. Required only if flow rate of system  
primary is excessive for size of boiler branch tees or if  
chilled water main is above boilers.  
13 System supply temperature thermometer.  
14 Boiler headers for three (3) boilers can be larger than pipe loop,  
if desired, to aid in balancing.  
Normal use of flow control valves is required to prevent cross  
circulation of zones as with any multiple pump system. Flow control  
is not required on boiler circuit.  
The system flow rate is selected to give the desired system  
temperature drop - depending on the design criteria.  
Attention should be given to balancing gas inputs and water flow  
rates. Large systems with multiple boilers should include main  
water temperature control (with or without outdoor reset) to stage  
the boilers on and off in relation to the load on the system.  
The boiler generator flow rates, on the other hand, should be  
selected to give the temperature rise through the generator that is  
both economical and offers the best generator efficiency.  
3. WATER SUPPLY LINE  
The boiler temperature rise is normally between 100C and 200C  
(200F and 400F). The system temperature that will be introduced  
to the boiler (inlet temperature) plus the selected boiler temperature  
rise selected from PUMPAND PIPE SIZING DATAshould not exceed  
the high limit control setting of 1150C (2400F).  
These boilers can be used ONLY in a forced circulation hot water  
heating system. Since most forced circulation systems will be of  
the closed type, install the water supply line as shown on piping  
diagrams, fig. 1 or 2.  
Fast filling of large pipe, old radiator installations and pressure  
purging of series loop systems (where high pressures are not  
available) requires bypassing of the pressure reducing valve.  
Generally, pressure purging is not possible with a well pump  
system. High point air venting is essential.  
There should be a relation of the minimum system load to the size  
boiler selected as the first firing or base boiler. This will stabilize  
operation during minimum load periods.  
B. Commercial Boiler Replacements  
If the system is of the open type, a pressure reducing valve will not  
be required as the water supply to the system will be controlled by  
a manually operated valve. An overhead surge tank is required.  
Application of LINEAR-TEMP® to a commercial boiler replacement  
with an old multiple pump installation is an excellent way to  
modernize the system. The A. O. Smith boiler(s) should be  
installed on a pipe loop with a separate circulating pump selected  
from PUMPAND PIPE SIZING DATATABLE.  
4. EXPANSION TANK  
CAUTION  
Figure 3 shows a line drawing of how the system headers should  
be connected to the pipe loop installed with the replacement  
boiler(s). Make-up water connections and accessories are not  
shown.  
A closed system will exist if a check valve (without bypass), pressure  
reducing valve (without bypass), or a water meter (without bypass)  
is installed in the cold water line between the water heater and  
street main (or well).  
8
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If the boiler is connected to chilled water piping or its heating coils  
are exposed to refrigerated air, the boiler piping system must be  
equipped with flow valves or other automatic means to prevent  
gravity circulation through the boiler during the cooling cycle.  
Excessive pressure may develop causing premature tank failure  
or intermittent relief valve operation. This is not a warranty failure.  
An expansion tank or a similar device may be required in the inlet  
supply line between the appliance and the meter or valve to  
compensate for the thermal expansion of water under supply  
pressure, see figure 1.  
8. CIRCULATING PUMP  
CONSTANT CIRCULATING PUMP OPERATION OF THE BOILER  
VOIDS THE WARRANTY. Constant water flow through the unit will  
“wash” away the copper’s natural protective coating. This is called  
velocity erosion. This erosion is not as great a problem when  
intermittent circulating operation is used per the recommended  
installation procedure. Constant circulation of water through the  
building’s system main is permissible as long as the water does  
not constantly flow through the boiler. Only all bronze or stainless  
steel circulators are to be used with the unit when it is installed in  
HOT WATER SUPPLY SYSTEMS.  
An air separator as shown in the piping diagrams is recommended  
especially for modern commercial hydronic systems.  
5. VENTVALVES  
It is recommended that automatic, loose key or screwdriver type  
vent valves be installed at each convector or radiator.  
6. MANIFOLD HEADERS  
Split systems with individual supply and return lines from the boiler  
room should normally have this piping connected to supply and  
return manifold headers near the boiler. To achieve good water  
distribution with maximum pressure drop for several circuits,  
manifolds of at least 2-1/2" (64mm) diameter are suggested on  
HWB/HW-399, HWB/HW-420, HWB/HW-520, HWB/HW-610 and  
HW-670 units. HWB/HW-300 units should have 1-1/2" (38mm)  
diameter manifolds.  
The circuits should be spaced on the header at a minimum of  
3" (76mm) center to center. Install a balancing cock in each return  
line.  
ATYPICALCIRCULATING PUMP  
FIGURE5  
Manifold headers are recommended for split systems with or  
without zone valves and also those installations with zone  
circulators. If the system is to be split at remote points, good  
practice requires special attention be given to main pipe sizing to  
allow balancing of water flow.  
Although each circulator that requires oiling is oiled and operated  
by the manufacturer, IT MUST BE OILED AGAIN BEFORE  
OPERATED. Oil the three oil cups (2 on the motor, 1 on the pump)  
as instructed on the oil tube supplied with the unit, fig 5.  
Thereafter, during the heating season, lubricate the three oil cups  
at least once every four months. Combination heating-cooling  
systems should be lubricated every four months year ‘round.  
The boiler piping system of a hot water boiler connected to heating  
coils located in air handling units where they may be exposed to  
refrigerated air circulation must be equipped with flow control valves  
or other automatic means to prevent gravity circulation of the boiler  
water during the cooling cycle.  
Use 2 or 3 teaspoonsful in bearing oil cups, fig. 5, and 10 or  
12 drops in the motor oil cups. Use No. 20 non-detergent motor  
oil.  
7. COOLING PIPING  
Follow the same oiling procedure if a replacement circulator is  
installed into the system.  
When the boiler is used in conjunction with a refrigeration system  
it must be installed so that the chilled medium is piped in parallel  
with the boiler with appropriate valves to prevent the chilled medium  
from entering the boiler, fig. 4.  
GAS CONNECTIONS  
WARNING  
THIS BOILER IS NOT INTENDED TO OPERATE AT GAS SUPPLY  
PRESSURE OTHER THAN SHOWN ON THE RATING PLATE.  
EXPOSURE TO HIGHER GAS SUPPLY PRESSURE MAY CAUSE  
DAMAGE TO GAS VALVES WHICH CAN RESULT IN FIRE OR  
EXPLOSION. IF OVERPRESSURE HAS OCCURRED SUCH AS  
THROUGH IMPROPER TESTING OF GAS LINES OR EMERGENCY  
MALFUNCTION OFTHE SUPPLYSYSTEM, THE GAS VALVES MUST  
BE CHECKED FOR SAFE OPERATION. MAKE SURE THAT THE  
OUTSIDE VENTS ON THE SUPPLY REGULATORS AND THE  
SAFETY VENT VALVESARE PROTECTEDAGAINSTBLOCKAGE.  
THESE ARE PARTS OF THE GAS SUPPLY SYSTEM, NOT THE  
BOILER. VENT BLOCKAGE MAY OCCUR DURING ICE BUILD-UP  
OR SNOW STORMS.  
Water temperature in the heating system must be reduced to less  
than 1000F (38°C) before cooling system is started, or damage to  
the chiller unit may occur.  
WHEN LOCAL CODES REQUIRE A MAIN MANUAL SHUTOFF  
VALVE OUTSIDE THE BOILER JACKET,ASUITABLE MAIN MANUAL  
SHUTOFF VALVE MUST BE INSTALLED IN A LOCATION  
COMPLYING WITH THOSE CODES.  
SCHEMATIC SHOWING PROPER PIPING ISOLATION  
OF THE BOILER FROM THE CHILLER  
FIGURE4  
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ITIS IMPORTANTTO GUARDAGAINST GAS VALVE FOULING FROM  
CONTAMINANTS IN THE GAS WAYS. SUCH FOULING MAYCAUSE  
IMPROPER OPERATION, FIRE OR EXPLOSION.  
2A.SIZING GAS SUPPLY LINE (For single boiler installations and  
for installations of multiples of two or three of same size boilers).  
Use table 6, or CAN/CSA B149.1-00 (latest recent edition) to size  
IF COPPER SUPPLY LINES ARE USED THEY MUST BE iron pipe or equivalent gas supply line. Table 6 is based on a  
CERTIFIED FOR GAS SERVICE.  
pressure drop of 0.3 inches of water and a specific gravity of 0.60  
approximately that of natural gas. (LP gas has an S.G. of about  
1.53). If the service pressure is five inches water column or less,  
use one pipe size larger than specified in table 6 in order to minimize  
pressure drop in the line.  
BEFORE ATTACHING THE GAS LINE BE SURE THAT ALL GAS  
PIPE IS CLEAN ON THE INSIDE.  
TO TRAPANY DIRTOR FOREIGN MATERIALIN THE GAS SUPPLY  
LINE, A DIRT LEG (SOMETIMES CALLED DRIP LEG or sediment  
trap) MUST BE INCORPORATED IN THE PIPING, SEE FIG. 1. The  
dirt leg must be readily accessible and not subject to freezing  
TABLE6  
MAXIMUM CAPACITYOF PIPE IN CUBIC FEET OF GAS PER  
HOUR (BASED UPONAPRESSURE DROP OF 0.3 INCH WATER  
COLUMNAND 0.6 SPECIFIC GRAVITY GAS)  
conditions.  
INSTALL  
IN  
ACCORDANCE  
WITH  
RECOMMENDATIONS OF SERVING GAS SUPPLIERS. (Refer to  
National Fuel Gas Code, ANSI Z223.1 and/or  
CAN/CSA-B 149.1-00 Installation Codes.  
Length  
Meters  
From Gas  
(Nominal Iron Pipe Size (Inches)  
1 1/4 1 1/2 2 1/2  
Meter 1/2 3/4  
1
2
3
4
To prevent damage, care must be taken not to apply too much  
torque when attaching gas supply pipe to gas valve gas inlet.  
3 (10) 132 278 520 1,050 1,600 3,050 4,800 8,500 17,500  
6 (20)  
9 (30)  
92 190 350 730 1,100 2,100 3,300 5,900 12,000  
73 152 285 590  
890 1,650 2,700 4,700 9,700  
760 1,450 2,300 4,100 8,300  
670 1,270 2,000 3,600 7,400  
610 1,150 1,850 3,250 6,800  
560 1,050 1,700 3,000 6,200  
530 990 1,600 2,800 5,800  
490 930 1,500 2,600 5,400  
460 870 1,400 2,500 5,100  
410 780 1,250 2,200 4,500  
380 710 1,130 2,000 4,100  
350 650 1,050 1,850 3,800  
12 (40) 63 130 245 500  
15 (50) 56 115 215 440  
18 ((60) 50 105 195 400  
21 (70) 46 96 180 370  
24 (80) 43 90 170 350  
27 (90) 40 84 160 320  
30 (100) 38 79 150 305  
38 (125) 34 72 130 275  
45 (150) 31 64 120 250  
53 (175) 28 59 110 225  
60 (200) 26 55 100 210  
Fittings and unions in the gas line must be metal to metal type.  
Apply joint compounds (pipe dope) sparingly and only to the male  
threads of pipe joints. Do not apply compound to the first two  
threads. Use compounds resistant to the action of liquefied  
petroleum gases.  
THE BOILER AND ITS GAS CONNECTIONS MUST BE LEAK  
TESTED BEFORE PLACING THE BOILER IN OPERATION. Use  
soap and water solution or other material acceptable for the  
purpose in locating gas leaks. DO NOT USE MATCHES, CANDLES,  
FLAME OR OTHER SOURCES OF IGNITION FOR THIS PURPOSE.  
320 610  
980 1,700 3,500  
*The heating value of Natural Gas is approximately 1,050 Btu/Ft.3.  
Propane (LP) Gas has a heating value of approximately 2,500 Btu/Ft3.  
1 cu. meter=35.31 cu. feet.  
DISCONNECT THE BOILER AND ITS MAIN MANUAL GAS  
SHUTOFF VALVE FROM THE GAS SUPPLY PIPING SYSTEM  
DURING ANY PRESSURE TESTING OF THE GAS SUPPLY  
SYSTEM OVER 1/2 PSIG (3.5kPa).. THE GAS SUPPLY LINE MUST  
BE CAPPED WHEN NOT CONNECTED TO THE BOILER.  
Where it is necessary to use more than the average number of  
pipe fittings i.e. elbows, tees, and valves in gas supply line, use a  
pipe larger than specified to compensate for increased pressure  
drop.  
2B. SIZING GAS SUPPLY LINE (For multiples of over three boilers  
of same size or for multiple installations of two or more mixed  
sizes).  
THE BOILER MUST BE ISOLATED FROM THE GAS SUPPLY  
PIPING SYSTEM BY CLOSING ITS MAIN MANUAL GAS SHUTOFF  
VALVE DURINGANY PRESSURE TESTING OF THE GAS SUPPLY  
PIPING SYSTEM AT TEST PRESSURES EQUAL TO OR LESS  
THAN 1/2 PSIG (3.5kPa).  
Capacities in cubic feet per hour of 0.60 specific gravity gas for  
different sizes and lengths are shown in table 6. No additional  
allowance is necessary for an ordinary number of fittings.  
PURGING  
Applications of the gravity factor converts the figures given in table  
6 to capacities with another gas of different specific gravity. Such  
application is accomplished by multiplying the capacities given in  
table 6 by the multipliers shown in table 7.  
Gas line purging is required with new piping or systems in which  
air has entered.  
CAUTION  
PURGING SHOULD BE PERFORMED BY PERSONS  
EXPERIENCED IN THIS TYPE GAS SERVICE TOAVOID RISK OF  
FIRE OR EXPLOSION. PURGE DISCHARGE MUST NOT ENTER  
CONFINEDAREAS OR SPACES WHERE IGNITION CAN OCCUR.  
THEAREAMUST BE WELLVENTILATED ANDALL SOURCES OF  
IGNITION MUST BE INACTIVATED OR REMOVED.  
To determine the size of each section of gas piping in a system  
within the range of table 6 proceed as follows:  
•
Determine the gas demand of each appliance to be attached  
to the piping system. When table 6 is to be used to select the  
piping size, calculate the gas demand in terms of cubic feet per  
hour for each piping system outlet. The gas demand for an  
appliance can be found by dividing its heat input rate by the  
gas’s heating value.  
1. CORRECT GAS  
Make sure the gas on which the boiler will operate is the same as  
that specified on the boiler rating plate. Do not install the boiler if  
equipped for a different type gas — consult your supplier.  
•
Obtain or determine the length of piping from the gas meter or  
service regulator to the appliance(s).  
10  
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•
•
In table 6, select the row showing the distance to the most  
remote outlet or the next longer distance if the table does not  
give the exact length. This is the only distance used in  
determining the size of any section of gas piping. If the gravity  
factor is to be applied, the values in the selected row of table 6  
are multiplied by the appropriate multiplier from table 7.  
TABLE 7  
MULTIPLIERS TO BE USED WITH TABLE 6 WHENAPPLYING  
THE GRAVITY FACTOR TO OTHER THAN .60 SPECIFIC GRAVITY  
Specific  
Gravity  
.35  
Specific  
Gravity  
1.00  
Multiplier  
1.31  
1.23  
1.16  
1.10  
1.04  
1.00  
.96  
Multiplier  
.78  
.40  
.45  
.50  
.55  
1.10  
1.20  
1.30  
1.40  
.74  
.71  
.68  
.66  
.63  
.61  
.59  
.58  
Total the gas demands of all appliances on the piping system.  
Enter table 6, on the left hand side, at the row equal to or just  
exceeding the distance to the most remote outlet. Select the  
pipe size in the row with a capacity equal to or just exceeding  
the total gas demand. This is the required main gas supply  
line size leading away from the gas meter or regulator. To  
determine the pipe size required for each branch outlet leading  
away from the main supply line, determine the gas demand for  
that outlet. Enter table 6 on the same row, and select the branch  
pipe size for a capacity equal to or just exceeding the demand  
at that outlet. The main line can be resized for a lesser capacity  
after each branch outlet, since the gas demand is reduced.  
Total the gas demands of all remaining appliances branching  
off downstream on the main gas line. Re-enter table 6 in the  
same row and select the appropriate pipe size with adequate  
capacity. Repeat the branch sizing and main line re-sizing for  
any remaining appliances in the system.  
*.60 (Nat.)  
.65  
*1.50 (Prop.)  
1.60  
.70  
.75  
.80  
.85  
.93  
.90  
.87  
.84  
1.70  
1.80  
1.90  
.56  
.55  
.54  
*2.00 (Butane)  
2.10  
.90  
.82  
*Use these correction factors if exact specific gravity of the gas is not  
known.  
GAS PRESSURE REGULATORS  
The gas pressure regulator is included in the combination gas  
valve, fig. 6, and is set to operate on the gas specified on the boiler  
model and rating plate.  
Periodically check main burner, fig. 41, and pilot flame, fig. 42, for  
proper operation. This should be checked every six months.  
Do not subject the gas valve to inlet gas pressures of more than  
14" W.C. (1/2 P.S.I.). If higher gas pressures are encountered, a  
service regulator is necessary.  
TABLE 8  
CORRECT MANIFOLD PRESSURE FOR FULL  
BOILER INPUT (IN INCHES OF WATER COLUMN)  
Model  
Number  
Rated  
Input  
Manifold Pressure  
Natural  
3.5  
Propane  
10.0  
HWB/HW-300  
HWB/HW-399  
HWB/HW-420  
HWB/HW-520  
HWB/HW-610  
HW-670 Nat.  
HW-670 Prop.  
300,000  
399,000  
420,000  
520,000  
610,000  
660,000  
670,000  
EXAMPLE  
3.2  
9.5  
3.5  
10.0  
Job Condition:  
3.5  
10.0  
3.5  
10.0  
Determining the required gas pipe size for a system composed of  
two HWB/HW-420 boilers and two HWB/HW-610 boilers to be  
installed as a multiple group, 50 lineal feet from meter. Gas to be  
used has a .60 specific gravity and heating value of 1,000 Btu per  
cubic foot.  
3.5  
10.0  
Adjustment, if required, is performed as follows:  
1. Set primary system temperature control dial (thermostat) at  
lowest setting so that boiler will not call for heat.  
Solution:  
2. Attach a pressure gauge to the tapping in the control string  
elbow.  
2 HWB/HW-420 Boilers  
2 HWB/HW-610 Boilers  
=
=
840,000 Btuh  
1,220,000 Btuh  
3. Reset primary system temperature control dial (thermostat)  
to highest setting. Main burner will now ignite.  
Total Btuh Input  
=
2,060,000 Btuh  
Total Btuh Input  
=
2,060,000 Btuh = 2,060 cf/h  
1,000  
4. With main burner firing, adjust pressure, if necessary, by turning  
pressure regulator adjusting screw with a screwdriver.  
Btu per Cubic Foot of Gas  
•
•
Clockwise to increase pressure.  
With a cubic foot per hour demand of 2,060 and with 50 lineal feet  
of gas supply line, table 6 shows a pipe size of 3" (76mm) is  
required.  
Counterclockwise to decrease pressure.  
5. Set primary system temperature control dial (thermostat) to  
lowest setting.  
NOTE: For other than .60 specific gravity, apply multiplier factor  
as shown in table 7.  
6. Remove pressure gauge and replace sealing plug.  
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7. Set primary system temperature control dial (thermostat) to Vent connectors serving appliances vented by natural draft shall  
desired setting.  
not be connected into any portion of mechanical draft systems  
operating under positive pressure.  
WARNING  
The minimum distance from adjacent public walkways, adjacent  
buildings, openable windows and building openings shall not be  
less than those values specified in the National Fuel Gas Code,  
ANSI Z223.1 and/or CAN/CSA B149.1-00, Installation Codes;  
DO NOT INCREASE GAS PRESSURE ABOVE THAT SPECIFIED  
ON THE RATING PLATE, AS OVERFIRING WILL RESULT IN  
DAMAGE TO THE BOILER, AS WELL AS INCREASED RISK OF  
FIRE, SOOTINGANDASPHYXIATION.  
Stack or chimney must be a minimum height of 12" (305mm)  
above the annual snow fall to prevent blockage.  
If gas pressure regulator cannot be adjusted to correct pressure  
with sufficient gas pressure at the valve, replace with new gas  
valve.  
Building materials must not come in contact with combustion  
products from stack or chimney, due to the degradating properties  
of flue products.  
VENTING THE BOILER - STANDARD VENTING  
WARNING  
Flue products must have a minimum clearance of 4 feet (1.22m)  
horizontally from, and in no case above or below, unless a 4-foot  
(1.22m) horizontal distance is maintained, from electric meters,  
gas meters, regulators and relief equipment.  
THE INSTRUCTIONS IN THIS SECTION ON VENTING THE  
BOILER MUST BE FOLLOWED TOAVOID CHOKED COMBUSTION  
OR RECIRCULATION OF FLUE GASES. SUCH CONDITIONS  
CAUSE SOOTING OR RISKS OF FIREANDASPHYXIATION.  
The Canadian B149.1-00, Installation Code specifies a 6 foot  
horizontal vent terminal clearance to gas and electric meters and  
relief devices (this clearance is specified as 4 feet in the U.S.  
under the National Fuel Gas Code, ANSI/Z223.1). Therefore  
instruction provision 134.1-b19(d), which specifies compliance  
with the 4 foot clearance, as applies in the U.S. only, and the  
B149.1-00 Installation Code applies in Canada.  
TYPE B VENTING MAY BE USED WITH THESE BOILERS. ALL  
LOCAL UTILITY REGULATIONS ON VENTING SHOULD BE  
FOLLOWED.  
1. DRAFT HOOD  
The draft hood furnished with this boiler must be installed without  
alteration. Provision must be made if the boiler is installed in  
confined space or a small boiler room to accommodate draft hood  
spillage and avoid risks described above. The upper air opening  
called for in the AIR REQUIREMENTS section of this manual is for  
this purpose.  
2. VENT CONNECTION  
ROBERTSHAW® 7000 DERHC  
HWB/HW-300, 399,-420, -520, -610, -670 NATURAL GAS WITH I.I.D.  
HW-300, -399, -420, -520, -670 LP GAS WITH I.I.D. U.S. ONLY  
Size and install proper size vent pipe. Do not reduce pipe size to  
less than that of the draft hood outlet.  
Horizontal runs of vent pipe shall be securely supported by  
adequately placed (approximately every 4 feet or 1 meter),  
noncombustible hangers and/or slip joints suitable for the weight  
and design of the materials employed to prevent sagging and to  
maintain a minimum upward slope of 1/4" (21mm/m) per foot  
from the boiler to the vent terminals, fig. 7. Dampers or other  
obstructions must not be installed in the vent. Be sure that the vent  
pipe does not extend beyond the inside wall of the chimney.  
ROBERTSHAW® 7000 ERHC (LP)  
HWB/HW-300, 399,-420, -520, -610 SINGLE STAGE  
STANDING PILOT, CANADIAN ONLY  
FIGURE6  
For boilers for connection to gas vents or chimneys, vent sizing,  
installation and termination shall be in accordance with Part 7,  
Venting of Equipment, of the National Fuel Gas Code, ANSI Z223.1,  
or Section 7, Venting Systems and Air Supply for Appliances, of the  
CAN/CSA B149.1-00, Installation Codes, or applicable provisions  
of the local building codes.  
VENT PIPE INSTALLATION  
FIGURE7  
® Robertshaw is a registered trademark of Fulton Controls Corp.  
12  
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Where a continuous or intermittent back draft is found to exist the  
cause must be determined and corrected. A special vent cap may  
be required. If the back draft cannot be corrected by the normal  
methods or if a suitable draft cannot be obtained, a blower type  
flue gas exhauster may be employed to ensure proper venting and  
correct combustion if permitted by local codes.  
After it has been determined that each appliance remaining  
connected to the common venting system properly vents when  
tested as outlined above, return doors, windows, exhaust fans,  
fireplace dampers and any other gas burning appliance to their  
previous conditions of use.  
Any improper operation of the common venting system should be  
corrected so the installation conforms with the latest edition of  
CAN/CGA B149.1-00 (latest edition). When resizing any portion of  
the common venting system, the common venting system should  
be resized to approach the minimum size as determined using  
the appropriate tables in Appendix G in CAN/CSA B149.1-00.  
WARNING  
FAILURE TO CORRECT BACK DRAFTS WILL CAUSE AIR  
CONTAMINATIONAND UNSAFE CONDITIONS.  
Vent connectors serving appliances vented by natural draft shall  
not be connected into any portion of mechanical draft systems  
operating under positive pressure.  
4. MULTIPLE VENTTABLE  
Table 9 has been compiled to show the material sizes in a Type B  
3. CONNECTING BOILER TO A COMMON VENT  
doublewall  
combined  
vent  
system.  
Refer  
to  
CAN/CSA B149 .1-00 (latest edition), or the ASHRAE 1983  
Equipment Volume for further information.  
Do not connect the boiler to a common vent or chimney with solid  
fuel burning equipment. This practice is prohibited by many local  
building codes as is the practice of venting gas fired equipment to  
the duct work of ventilation systems.  
A combined vent system is one in which two or more boilers at one  
level are attached to a common vent.  
Where a separate vent connection is not available and the vent  
pipe from the boiler must be connected to a common vent with oil  
burning equipment, the vent pipe should enter the common vent  
or chimney at a point ABOVE the flue pipe from the oil fired unit.  
In order to use table 9, the connector rise and total vent height  
must be known. Connector rise is vertical distance from the draft  
hood outlet to the point where the manifold connection is made.  
Total vent height is the least vertical distance from a draft hood  
outlet to the top of the vent. Local codes or utility requirements  
often govern termination height. ULC listed doublewall gas vents,  
up through 24" (610mm) diameter, can be installed in heated and  
unheated areas and can pass through floors, ceilings, partitions,  
walls and roofs, provided the required one inch clearance is  
observed. These vents should be installed in accordance with  
CAN/CSA B149.1-00 (latest edition).  
Where two or more appliances vent into a common vent connector  
or manifold, the area of the common vent or vent connector should  
at least equal the area of the largest vent connector plus 50% of  
the areas of the additional draft hood outlets.  
When removing a boiler from a system with a common vent, use  
the following steps:  
EXAMPLE SHOWING USE OF THE HWB/HW-610 COMBINED VENT  
SIZING TABLE 9  
Be sure the other appliances connected to the common vent are  
not in operation.  
Seal any unused openings in the common venting system.  
Visually inspect the venting system for proper size and horizontal  
pitch and determine there is no blockage or restriction, leakage,  
corrosion and other deficiencies which could cause an unsafe  
condition.  
WARNING  
Ensure sufficient supply and ventilation air. Under no circumstances  
should the equipment room where the boiler is installed ever be  
under negative pressure. Insufficient air supply can interfere with  
combustion and ventilation of this boiler resulting in unsafe  
conditions.  
Insofar as is practical, close all building doors and windows and  
all doors between the space in which the appliances remaining  
connected to the common venting system are located and other  
spaces of the building. Turn on clothes dryers and any appliance  
not connected to the common venting system. Turn on any exhaust  
fans, such as range hoods and bathroom exhausts, so they will  
operate at maximum speed. Close fireplace dampers.  
Place in operation the appliance being inspected. Follow the  
lighting instructions. Adjust thermostat so appliance will operate  
continuously.  
Test for spillage at the draft hood relief opening after five minutes  
of main burner operation. Use the flame of a match or candle.  
FIGURE8  
13  
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TABLE 9, COMBINED VENT SIZING TABLES  
MODEL HW/HWB-300 BOILER  
MODEL HW/HWB-610 BOILER  
Input: 300,000 Btuh  
Required Connector or Smoke Pipe Diameter  
Connector Total Vent Height(Measured in Feet Above Draft Hood)  
Draft Hood Outlet 8"  
Input: 610,000 Btuh  
Required Connector or Smoke Pipe Diameter  
Connector Total Vent Height(Measured in Feet Above Draft Hood)  
Draft Hood Outlet 12"  
Rise in  
Feet  
10  
15  
20  
30  
40  
50  
60  
80 100  
Rise in  
Feet  
10  
15  
20  
30  
40  
50  
60  
80 100  
Connector Diameter (in Inches)  
Connector Diameter (in Inches)  
1
2
3
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
10  
1
2
3
16  
14  
14  
12  
14  
14  
14  
12  
14  
14  
12  
12  
14  
14  
12  
12  
14  
14  
12  
12  
14  
12  
12  
12  
14  
12  
12  
12  
14  
12  
12  
12  
14  
12  
12  
12  
4 or more  
Total  
Input  
Btuh x 1000  
600  
4 or more  
Total  
Number  
if Units  
Combined  
Total Vent Height(Measured in Feet Above Draft Hood)  
10 15 20 30 40 50 60 80 100  
Manifold and Common Vent Diameter (in Inches)*  
14  
16  
18  
Number  
if Units  
Combined  
Total Vent Height(Measured in Feet Above Draft Hood)  
10 15 20 30 40 50 60 80 100  
Manifold and Common Vent Diameter (in Inches)*  
Input  
Btuh x 1000  
1220  
1830  
2440  
3050  
3660  
4270  
4880  
5490  
6100  
6710  
7320  
2
3
4
12  
14  
16  
12  
14  
16  
12  
14  
14  
10  
12  
14  
10  
12  
14  
10  
12  
14  
10  
12  
12  
10  
12  
12  
2
3
4
5
6
7
8
9
18  
22  
26  
28  
32  
34  
36  
38  
40  
42  
44  
18  
20  
24  
26  
28  
32  
34  
36  
38  
38  
42  
16  
20  
22  
26  
28  
30  
32  
34  
36  
38  
38  
16  
18  
20  
24  
26  
28  
30  
30  
32  
34  
36  
14  
18  
20  
22  
24  
26  
28  
30  
30  
32  
34  
14  
16  
18  
22  
24  
24  
26  
28  
30  
30  
32  
14  
16  
18  
20  
22  
24  
26  
28  
28  
28  
32  
14  
16  
18  
20  
22  
22  
24  
26  
26  
28  
30  
14  
14  
16  
18  
20  
22  
24  
24  
26  
26  
28  
900  
1200  
MODEL HW/HWB-399 BOILER  
Input: 399,000 Btuh  
Draft Hood Outlet 10"  
Required Connector or Smoke Pipe Diameter  
Connector Total Vent Height(Measured in Feet Above Draft Hood)  
10  
11  
12  
Rise in  
Feet  
10  
15  
20  
30  
40  
50  
60  
80 100  
Connector Diameter (in Inches)  
1
2
3
12  
12  
12  
10  
12  
12  
10  
10  
12  
12  
10  
10  
12  
10  
10  
10  
12  
10  
10  
10  
12  
10  
10  
10  
12  
10  
10  
10  
12  
10  
10  
10  
12  
10  
10  
10  
4 or more  
Total  
Input  
Btuh x 1000  
798  
Number  
if Units  
Total Vent Height(Measured in Feet Above Draft Hood)  
10 15 20 30 40 50 60 80 100  
Manifold and Common Vent Diameter (in Inches)*  
14  
18  
20  
MODEL HW/HWB-670 BOILER  
Input: 660,000 or 670,000 Btuh  
Required Connector or Smoke Pipe Diameter  
Connector Total Vent Height(Measured in Feet Above Draft Hood)  
Draft Hood Outlet 12"  
Combined  
2
3
4
14  
16  
20  
14  
16  
18  
12  
14  
16  
12  
14  
16  
12  
14  
16  
12  
14  
14  
12  
14  
14  
12  
12  
14  
1197  
1596  
Rise in  
Feet  
10  
15  
20  
30  
40  
50  
60  
80 100  
Connector Diameter (in Inches)  
1
2
3
16  
14  
14  
12  
14  
14  
14  
12  
14  
14  
12  
12  
14  
14  
12  
12  
14  
14  
12  
12  
14  
12  
12  
12  
14  
12  
12  
12  
14  
12  
12  
12  
14  
12  
12  
12  
MODEL HW/HWB-420 BOILER  
Input: 420,000 Btuh  
Draft Hood Outlet 10"  
Required Connector or Smoke Pipe Diameter  
Connector Total Vent Height(Measured in Feet Above Draft Hood)  
4 or more  
Total  
Number  
if Units  
Combined  
Total Vent Height(Measured in Feet Above Draft Hood)  
10 15 20 30 40 50 60 80 100  
Manifold and Common Vent Diameter (in Inches)*  
Input  
Btuh x 1000  
1340  
2010  
2680  
3350  
4020  
4690  
5360  
6030  
6700  
7370  
8040  
Rise in  
Feet  
10  
15  
20  
30  
40  
50  
60  
80 100  
Connector Diameter (in Inches)  
2
3
4
5
6
7
8
9
18  
22  
26  
28  
32  
34  
36  
38  
40  
42  
46  
18  
20  
24  
26  
28  
32  
34  
36  
38  
38  
44  
16  
20  
22  
26  
28  
30  
32  
34  
36  
38  
40  
16  
18  
20  
24  
26  
28  
30  
30  
32  
34  
38  
14  
18  
20  
22  
24  
26  
28  
30  
30  
32  
36  
14  
16  
18  
22  
24  
24  
26  
28  
30  
30  
34  
14  
16  
18  
20  
22  
24  
26  
28  
28  
28  
34  
14  
16  
18  
20  
22  
22  
24  
26  
26  
28  
32  
14  
14  
16  
18  
20  
22  
24  
24  
26  
26  
30  
1
2
3
12  
12  
12  
10  
12  
12  
10  
10  
12  
12  
10  
10  
12  
10  
10  
10  
12  
10  
10  
10  
12  
10  
10  
10  
12  
10  
10  
10  
12  
10  
10  
10  
12  
10  
10  
10  
4 or more  
Total  
Input  
Btuh x 1000  
840  
Number  
if Units  
Combined  
Total Vent Height(Measured in Feet Above Draft Hood)  
10 15 20 30 40 50 60 80 100  
Manifold and Common Vent Diameter (in Inches)*  
14  
18  
20  
2
3
4
14  
16  
20  
14  
16  
18  
12  
14  
16  
12  
14  
16  
12  
14  
16  
12  
14  
14  
12  
14  
14  
12  
12  
14  
10  
11  
12  
1260  
1680  
MODEL HW/HWB-520 BOILER  
Input: 520,000 Btuh  
Draft Hood Outlet 10"  
Required Connector or Smoke Pipe Diameter  
Connector Total Vent Height(Measured in Feet Above Draft Hood)  
Known: (5) model HWB/HW-610 boilers. (See illustration).  
Connector rise - 2' (Note 1' is minimum). Total vent height  
30'.  
Rise in  
Feet  
10  
15  
20  
30  
40  
50  
60  
80 100  
Connector Diameter (in Inches)  
1
2
3
14  
12  
12  
12  
14  
12  
12  
12  
14  
12  
12  
12  
12  
12  
12  
12  
12  
12  
10  
10  
12  
12  
10  
10  
12  
12  
10  
10  
12  
12  
10  
10  
12  
12  
10  
10  
Problem:  
Determine diameter of connector, manifold and  
common vent.  
4 or more  
Total  
Number  
if Units  
Combined  
Total Vent Height(Measured in Feet Above Draft Hood)  
10 15 20 30 40 50 60 80 100  
Manifold and Common Vent Diameter (in Inches)*  
16  
20  
22  
26  
28  
30  
32  
Input  
Btuh x 1000  
1040  
1560  
2080  
2600  
3120  
3640  
4160  
Procedure: Enter the top of the HWB/HW-610 table (total vent height)  
at 30' and the side at 2' (connector rise). A 14" connector  
diameter is indicated for each connector rise.  
2
3
4
5
6
7
8
16  
18  
22  
24  
26  
28  
30  
14  
18  
20  
22  
24  
26  
28  
14  
16  
18  
20  
22  
24  
26  
14  
16  
18  
20  
22  
24  
24  
14  
14  
18  
18  
20  
22  
24  
12  
14  
16  
18  
20  
22  
22  
12  
14  
16  
18  
18  
20  
22  
12  
14  
14  
18  
18  
20  
20  
To determine the manifold and common vent size, enter this table  
(total vent height) at 30 and the side at 5 boilers. A manifold  
diameter of 24" (610mm) is indicated.  
14  
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gas vent properly by passing a lighted match or taper around  
the edge of the relief opening of the draft hood. If the chimney or  
gas vent is drawing properly, the match flame will be drawn into  
the draft hood. If not, the combustion products will tend to  
extinguish this flame. IF THE COMBUSTION PRODUCTS ARE  
ESCAPING FROM THE RELIEF OPENING OF THE DRAFT  
HOOD, DO NOT OPERATETHE EQUIPMENT UNTILPROPER  
ADJUSTMENT OR REPAIRS ARE MADE TO PROVIDE  
ADEQUATE DRAFT THROUGH THE CHIMNEY OR GAS VENT.”  
VENTING MAINTENANCE - STANDARD VENTING  
It is recommended that the heating surfaces and vent piping of  
the appliance be checked every six months for dust, deterioration  
and carbon deposits. Remove all soot or other obstructions from  
chimney and flue which will retard free draft. Replace any  
damaged or deteriorated parts of the venting system.  
Qualified servicers should follow this procedure when the boiler’s  
external heating surfaces and vent pipe need cleaning.  
D. Next, turn on all other fuel burning appliances within the same  
room so they will operate at their full input.  
CAUTION  
DO NOT USE A NYLON BRUSH OR OTHER STATIC CREATING  
Repeat step C above, checking the draft on each appliance.  
MATERIAL TO CLEAN DUST AND CARBON DEPOSITS FROM  
HEATING SURFACESAND VENT.  
SUCH DEPOSITS ARE FLAMMABLE AND MAY BE IGNITED BY  
STATIC ELECTRICITY. USEAMETAL BRUSH TO MINIMIZE THE  
DANGER OF EXPLOSION.  
1. Turn off the electrical power (main manual gas shutoff and  
pilot valves, if applicable).  
FIGURE9  
Allow boiler parts and vent to cool before disassembly.  
2. Remove the boiler draft diverter and vent pipe running to the  
chimney.  
SAFETY RELIEF VALVES  
Your local code authority may have other specific relief valve  
requirements not covered below.  
•
Check parts and chimney for obstructions and clean as  
necessary.  
3. Remove burner from boiler and other metal parts as required  
to clean and vacuum the heat exchanger and combustion  
coils.  
WARNING  
THE PURPOSE OF A SAFETY RELIEF VALVE IS TO AVOID  
EXCESSIVE PRESSURE OR TEMPERATURE INTO THE STEAM  
RANGE WHICH MAY CAUSE SCALDING AT FIXTURES, TANK  
EXPLOSION, SYSTEM OR BOILER DAMAGE.  
•
Refer to parts list supplied with this manual for  
disassembly aid.  
4. Reinstall the parts removed in steps 2 and 3.  
TO AVOID SCALDING OR WATER DAMAGEA DRAIN LINE MUST  
BE CONNECTED TO A RELIEF VALVE TO DIRECT DISCHARGE  
TO A SAFE LOCATION. A DRAIN LINE MUST NOT BE REDUCED  
FROM THE SIZE OF THE VALVE OUTLET AND IT MUST NOT  
CONTAINANY VALVES BETWEEN THE BOILERAND THE RELIEF  
•
Be sure the vent pipe has a minimum upward pitch of one  
quarter inch per foot of length (21mm/m) and is sealed as  
necessary.  
5. Restore electrical power and gas supply to boiler.  
•
Place boiler in operation by following the lighting VALVE OR THE RELIEF VALVEAND THE DRAIN EXIT. INADDITION,  
instructions in this manual. THERE SHOULD NOT BE ANY RESTRICTIONS IN A DRAIN LINE  
•
Check for gas leaks and proper boiler and vent operation. NOR SHOULD IT BE ROUTED THROUGH AREAS WHERE  
FREEZING CONDITIONS MIGHT OCCUR. DO NOT THREAD OR  
CAPTHE DRAIN LINE EXIT. RESTRICTING OR BLOCKINGADRAIN  
LINE WILL DEFEAT THE PURPOSE OF THE RELIEF VALVE AND  
MAY CREATE AN UNSAFE CONDITION. INSTALL A DRAIN LINE  
WITHADOWNWARD SLOPE SUCH THAT IT NATURALLY DRAINS  
ITSELF.  
VENTING - SIDEWALL  
(OPTIONAL) POWER VENT SYSTEM  
If you are installing the optional Power Vent Kit, refer to your  
HWB/HW Power Vent Kit Installation Instructions for proper wiring  
and installation procedures. Contact your local A.O. Smith  
representative for details.  
If any safety relief valve is replaced, the replacement valve must  
comply with the latest version of the ASME Boiler and Pressure  
Vessel Code, Section IV or CSA B51, as applicable. Select a relief  
valve with a discharge NOT less than the boiler input, and a pressure  
rating NOT exceeding the working pressure of any component in  
the system.  
VENTING SYSTEM  
HAVE VENTING SYSTEM CHECKED EVERY SIX MONTHS FOR  
OBSTRUCTIONSAND/OR DETERIORATION IN VENT PIPING.  
A. O. Smith supplies Canadian HW boilers for hot water supply  
systems with a 125 psi pressure relief valve. This valve must be  
installed in the water outlet as near to the boiler as possible.  
A. Insofar as is practical, close all doors, windows and air inlets  
to the building. Turn on all exhaust fans (range hood,  
bathroom exhaust, etc.) so they will operate at their maximum  
speed. Close fireplace dampers.  
A. O. Smith United States HW and Canadian HWB boilers for space  
heating are shipped with a 50 psi pressure relief valve. This valve  
must be installed in the water outlet as near to the boiler as possible.  
B. After allowing appliance to operate for five minutes, test for  
spillage at the draft hood relief opening.  
C. “CHECKING THE DRAFT. Operate vent connected gas An ASME rated temperature and pressure relief valve must be  
utilization equipment for several minutes and check to see installed on each and every water storage tank in a hot water supply  
that the combustion products are going up the chimney or system.  
15  
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The boiler, when installed, must be electrically bonded to ground  
in accordance with the requirements of the authority having  
jurisdiction or, in the absence of such requirements, with the  
National Electrical Code, ANSI/NFPA 70 and/or the Canadian  
Electrical Code Part 1, CSA C22.1, Electrical Code.  
The storage tank temperature and pressure (T & P) relief valve  
must comply with the applicable construction provisions of the  
Standard for Relief Valves and Automatic Gas Shutoff Devices for  
Hot Water Supply Systems, Z21.22 and/or CAN1-4.4. The T & P  
valve must be of the automatic reset type and not embody a  
single-use type fusible plug, cartridge or linkage.  
STRICT ADHERENCE TO PIPING AND WIRING DIAGRAMS IS  
REQUIRED TO PREVENT CONSTANT PUMP OPERATION WHEN  
SYSTEM TEMPERATURE CONTROLIS SATISFIED. OTHERWISE  
THE WARRANTY IS VOID AS STIPULATED IN THE LIMITED  
WARRANTY ON THE INSTRUCTIONS MANUAL.  
The T & P relief valve should have a maximum temperature rating  
of 1000C (2100F), a pressure rating NOT exceeding the lowest  
rated working pressure of any system component, and a discharge  
capacity exceeding the total input of the water boilers supplying  
water to the storage tank.  
The electrical connections must be made so that the circulator will  
operate before the gas valve opens. At no time may the controlling  
system allow the burner to fire when there is no water flow through  
the boilers.  
Locate the T & P relief valve (a) in the top of the storage tank, or (b)  
in the side of the tank on centerline within the upper 6 inches from  
the top of the tank. See figures 20 to 31. Tapping shall be threaded  
in accordance with the latest version of the Standard for Pipe  
Threads, General Purpose (inch), ANSI/ASME B1.20.1  
Refer to the diagrams in fig’s. 10 thru 11C for proper wiring  
sequence with conventional single boiler installations.  
Mark location with a Class lll label.  
The THERMAL BALANCER shown is factory included by  
A. O. Smith as part no. 98190. This device serves as a pump  
shutdown delay switch to balance the rising boiler water  
temperature to system temperature before the pump stops.  
Overshooting of boiler temperature is prevented and stack loss  
after shutdown is negligible.  
See ANSI Z21.10.1, Part 1, MARKING, See CAN/CSA B149.1-00.  
WIRING CONNECTIONS  
CAUTION  
LABEL ALL WIRES PRIOR TO DISCONNECTION WHEN  
SERVICING CONTROLS. WIRING ERRORS CAN CAUSE  
IMPROPERAND DANGEROUS OPERATION.  
WARNING  
AN ELECTRICAL GROUND IS REQUIRED TO REDUCE RISK OF  
ELECTRIC SHOCK OR POSSIBLE ELECTROCUTION. Make the  
ground connection to the screw provided in the electrical supply  
junction box on the boiler.  
VERIFY PROPER OPERATIONAFTER SERVICING.  
1. CONVENTIONALINSTALLATIONS  
IF ANY OF THE ORIGINAL WIRE, AS SUPPLIED WITH THE  
ALLELECTRICALWORK MUST BE INSTALLED INACCORDANCE APPLIANCE, MUST BE REPLACED, IT MUST BE REPLACED WITH  
WITH NATIONALELECTRICALCODE,ANSI/NFPA70AND/ORTHE TYPE 1050C WIRE OR ITS EQUIVALENT, EXCEPTFOR THE FLAME  
CANADIAN ELECTRICALCODE, PART1, CSAC22.1, ELECTRICAL SENSOR AND IGNITION CABLE WHICH ARE 2500C AND WIRES  
CONNECTED TO THE COIL PROTECTOR WHICH ARE 2000C.  
CODEAND MUST CONFORM TO LOCAL REGULATIONS.  
16  
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SINGLE STAGE I.I.D. - ROBERTSHAW® GAS VALVE  
HWB & HW-300, -399, -420, -520, -610 (NATURAL GAS ONLY) - CANADIAN MODELS  
FIGURE 10  
® Robertshaw is a registered trademark of Fulton Controls Corp.  
17  
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SINGLE STAGE PROPANE - ROBERTSHAW GAS VALVE  
24 VOLT -HW, HWB-420, -520, -610 CANADIAN MODELS  
FIGURE11  
18  
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CONNECTION DIAGRAM HWB & HW 300, 399  
(PROPANE GAS)  
FIGURE 13  
SINGLE STAGE PROPANE ROBERTSHAW GAS VALVE  
24 VOLT - HWB, HW-300, 399 CANADIAN MODELS  
FIGURE11A  
19  
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HW-300, HW-399, HW-420, HW-500 & HW-670  
(NATURALGAS)  
SINGLE STAGE I.I.D. - ROBERTSHAW GAS VALVE  
HW-300, -399, -420, -520 & 670 (NATURAL GAS ONLY) - U.S. MODELS  
FIGURE11B  
20  
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HW-300, HW-399, HW-420, HW-500 & HW-670  
(PROPANE GAS)  
FIGURE 12  
SINGLE STAGE I.I.D. - ROBERTSHAW GAS VALVE  
HW-300, -399, -420, -520 & 670 (PROPANE GAS ONLY) - U.S. MODELS  
FIGURE11C  
21  
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TYPICAL WIRING DIAGRAM (IID NATURAL GAS) FOR SINGLE BOILERLINEAR-TEMP® INSTALLATION FOR CANADIAN MODELS  
FIGURE 12  
Space temperature controlling can be varied to meet the building  
requirements. Either the single thermostat, as shown, or multiple  
2. LINEAR-TEMP INSTALLATIONS  
Control for these systems is decided mainly by the type of building zone thermostats should control a common relay. This relay  
system controlling that is desired. A single boiler installation might  
be controlled directly from space temperature thermostat(s).  
Multiple boiler installations are more effective when the boilers  
are sequenced in and out of operation by some form of main water  
temperature controller. With one to three boilers, individual controls  
set at progressive temperatures may be used. For more than  
three or four boilers, a step controller is recommended.  
controls electric power to the system primary circulator and to the  
main water temperature controller. This provides for water  
movement in the system before the main temperature controller  
can start the secondary circulating pump or fire the boiler.  
Figure 12 shows a typical wiring diagram for a single boiler space  
heating installation. The boiler may be controlled by a main  
temperature controller as shown or may include outdoor reset if  
desired. The boiler shown is the model HW-610 with single stage  
firing, typical of HW models.  
Individual boiler controls, or the separate stages of a step controller,  
should fire a boiler and also start the boiler loop circulator whenever  
the first boiler of a group supplied by that boiler loop is fired. Some  
large installations may require the firing of more than one boiler  
per stage.  
Figure 13 shows a layout for various choices of controls often  
found in commercial heating. These layouts are not intended to  
be wiring diagrams and only show the relation of one device to  
another in the system.  
The system or primary circulator may or may not be controlled by  
the boiler sequencer. When this pump is operated through the  
first switch of any type of step controller, care should be taken to  
determine if a motor starter is needed due to insufficient switch  
capacity.  
Figure 13 is a typical layout of controls for two boilers with one  
circulator and including optional outdoor reset and thermal  
balancer. If a secondary circulator is used with each boiler,  
arrangement for boiler no. 2 will be as shown for boiler no. 1.  
If the primary pump is controlled by a manual switch or any other  
controllers, the electric current supply to the boiler group should  
be through the primary pump controller. The fast response of  
A. O. Smith boilers eliminates any need to maintain boiler  
temperature when the system is satisfied. Wiring should always  
prevent firing of boiler(s) when there is no water flow in the mains.  
Commercial size installations are always best when designed to  
individual building requirements.  
The layout in figure 13 is typical of many combination possibilities  
to meet the requirements of different buildings. Brand names of  
controls shown are suggestions and not directly related to any  
particular type of system. THESE LAYOUTS ARE NOT WIRING  
DIAGRAMS.  
Installation diagrams show flow switches in the outlet piping from  
each boiler as good protection against any boiler being fired when  
the boiler loop circulator is not in operation. These flow switches  
will also serve as protection if there is a loss of water.  
A.O. Smith offers accessory Sequencing Control Panels;  
TEK-252 for 2 Stage Boiler Control  
Outdoor vent systems will normally require an automatic shutdown  
control if there is a continuous recirculating main and/or if the  
entire building is not under control of space temperature  
thermostats. A single bulb outdoor sensing control will prevent  
overheating of halls, stairways or other uncontrolled areas. There  
are occasions when outdoor temperatures are temporarily too  
warm for even a moderate amount of heating in these areas.  
TEK-254 for 4 Stage Boiler Control  
TEK-258 for 8 stage Boiler Control  
For more information contact A.O. Smith Product Service  
Department at 1-800-433-2545.  
22  
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NOTE:  
3. Outdoor thermostat required if building controls do not provide automatic  
shutdown of reset controls during warm weather.  
Boilers and Secondary Circulator are Controlled by  
• Dual Bulb, Dual Switch Controller  
1. Building temperature controls supply electric power to building  
circulator.  
2. Main flow switch proves main water flow before energizing sequencing  
and resetting controls.  
Staging and Outdoor Reset of Main Water Temperature  
CONTROLAPPLICATION DIAGRAM - TWO BOILER LINEAR-TEMP® INSTALLATION WITH TWO CIRCULATORS  
FIGURE 13  
NOTE:  
Boilers and Secondary Circulator are Controlled by  
1. Building temperature controls supply electric power to building  
circulator.  
• One Dual Bulb, Dual Switch Mechanical Controller and  
• One Dual Bulb, single Switch Mechanical Controller  
2. Main flow switch proves main water flow before energizing sequencing  
and resetting controls.  
3. Outdoor thermostat required if building controls do not provide automatic  
shutdown of reset controls during warm weather.  
Sequencing and Outdoor Reset of Main Water Temperature.  
CONTROLAPPLICATION DIAGRAM - THREE BOILER LINEAR-TEMP® INSTALLATION WITH THREE CIRCULATORS  
FIGURE 14  
23  
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NOTE:  
1. Building temperature controls supply electric  
power to building circulator.  
2. Main flow switch proves main water flow before  
energizing sequencing and resetting controls.  
3. Outdoor thermostat required if building controls  
do not provide automatic shutdown of reset  
controls during warm weather.  
Boilers and Secondary  
Circulator are Controlled by  
Dual Bulb, Dual Switch Controller  
Staging and Outdoor Reset of  
Main Water Temperature  
CONTROLAPPLICATION DIAGRAM - FOUR BOILER LINEAR-TEMP® INSTALLATION WITH TWO CIRCULATORS  
FIGURE 15  
NOTE:  
1. Building temperature controls  
supply electric power to  
building circulator.  
2. Main flow switch proves main  
water flow before energizing  
sequencing and resetting  
controls.  
3. Outdoor thermostat required if  
building controls do not provide  
automatic shutdown of reset  
controls during warm weather.  
4. Should motor load exceed 7.5  
AMPS,  
use relays or motor starters.  
5. In absence of main flow switch  
and low water cutoff, jumper  
"A" and "B" together.  
Boilers and Secondary Circulator areControlled by Dual Bulb, Dual Switch Controller Staging and Outdoor Reset of Main Water Temperature  
CONTROLAPPLICATION DIAGRAM - EIGHT BOILER LINEAR-TEMP® INSTALLATION WITH INDIVIDUAL CIRCULATORS  
FIGURE 16  
24  
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CER-TEMP 80 - 1 UNIT INSTALLATION - FOR HOT WATER SUPPLY APPLICATION  
CANADIAN MODELS, JUNCTION BOX W/6 TERMINALS  
FIGURE 17  
CER-TEMP 80 - 1 UNIT INSTALLATION - FOR HOT WATER SUPPLY APPLICATION  
U.S. MODELS, JUCNTION BOX W/4 TERMINALS  
FIGURE 18  
FIGURE 19  
25  
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CER-TEMP 80 - 2 OR 3 UNIT INSTALLATION - FOR HOT WATER SUPPLY APPLICATION  
CANADIAN MODELS, JUNCTION BOX W/6 TERMINALS  
FIGURE 20  
26  
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SCHEMATIC  
CANADIAN MODELS, JUNCTION BOX W/6 TERMINALS  
27  
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CER-TEMP 80 - 2 OR 3 UNIT INSTALLATION CONNECTION DIAGRAM  
(FOR HOT WATER SUPPLY APPLICATION)  
U.S. MODELS, JUNCTION BOX W/4 TERMINALS  
FIGURE 22  
28  
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CER-TEMP 80 - 2 OR 3 UNIT INSTALLATION SCHEMATIC DIAGRAM  
(FOR HOT WATER SUPPLY APPLICATION)  
U.S. MODELS, JUNCTION BOX W/4 TERMINALS  
FIGURE 23  
29  
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BOOSTER - RECOVERY WIRING DIAGRAM  
CANADIAN MODELS, JUNCTION BOX W/6 TERMINALS  
FIGURE 24  
SHURE-TEMP BOOSTER - RECOVERY WIRING DIAGRAM  
(TWO TEMPERATURE SYSTEM)  
CANADIAN MODELS, JUNCTION BOX W/6 TERMINALS  
FIGURE 25  
30  
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BOOSTER - RECOVERY WIRING DIAGRAM  
U.S. MODELS, JUNCTION BOX W/4 TERMINALS  
FIGURE 26  
SHURE - TEMP BOOSTER - RECOVERY WIRING DIAGRAM  
TWO-TEMPERATURE SYSTEM  
U.S. MODELS, JUNCTION BOX W/4 TERMINALS  
FIGURE 27  
31  
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TANK TEMPERATURE CONTROL  
WATER LINE CONNECTIONS  
This section provides detailed installation diagrams for typical  
methods of application for the unit using a Cer-Temp 80 Recovery  
System (for one temperature water), and either Booster-Recovery  
or the Shure-Temp Booster-Recovery System (for two temperature  
water).  
The water temperature in the storage tank is controlled by the Tank  
Temperature Control. The sensing element is mounted inside  
the hot water storage tank, see fig's. 31-38.  
DANGER  
HOT WATER TEMPERATURES REQUIRED FOR AUTOMATIC  
DISHWASHER AND LAUNDRY USE CAN CAUSE SCALD BURNS  
RESULTING IN SERIOUS PERSONAL INJURY AND/OR DEATH.  
THE TEMPERATUREAT WHICH INJURY OCCURS VARIES WITH  
THE PERSON’S AGE AND TIME OF EXPOSURE. THE SLOWER  
RESPONSE TIME OF CHILDREN, AGED OR DISABLED  
These diagrams will serve to provide the installer with a reference  
for the materials and methods of piping necessary for installation.  
It is essential that all water and gas piping, vent connections,  
electrical wiring, and check and flow regulating valves be installed  
as shown on the diagrams.  
Consult the installation diagrams for appropriate locations to install PERSONS INCREASES THE HAZARDS TO THEM. NEVER ALLOW  
the safety flow switch(es), drain valves, thermometers, relief valves  
and the circulating pump(s). Apply suitable pipe thread sealing  
compounds to only the male threads of parts to be connected.  
If any of these parts are being replaced in a functioning system,  
remember to shut off the manual gas and control valve(s) and  
close off the water inlet(s). Open a nearby faucet to relieve pressure  
and/or drain the boiler or system before attempting to install the  
new parts.  
SMALL CHILDREN TO USE A HOT WATER TAP, OR TO DRAW  
THEIR OWN BATH WATER. NEVER LEAVEACHILD OR DISABLED  
PERSON UNATTENDED IN A BATHTUB OR SHOWER.  
Check the diagrams thoroughly before starting installation to avoid  
errors and minimize time and materials cost.  
If the system is to be filled with water for testing or other purposes  
during cold weather and before actual operation, care must be  
taken to prevent a downdraft entering the boiler or freezing air from  
contacting the system. Failure to do so may cause the water in the  
system to freeze with resulting damage to the system. Damage  
due to freezing is not covered by the warranty.  
The tank temperature control is adjustable from 100°F (37.7°C) to  
220°F (104.4°C). It is recommended that lower water temperatures  
be used to avoid the risk of scalding. It is further recommended, in  
all cases, that the water temperature be set for the lowest  
temperature which satisfies the user’s hot water needs. This will  
also provide the most energy efficient operation of the water heater  
and minimize scale formation.  
This equipment must be protected against loss of water or loss of  
water flow by the installation of a safety flow switch in the outlet  
piping from the boiler. Piping and wiring diagrams show the  
application of the accessory package for this purpose.  
THE WATER HEATER SHOULD BE LOCATED INANAREAWHERE  
THE GENERAL PUBLIC DOES NOT HAVE ACCESS TO SET  
TEMPERATURES. SETTING THE WATER TEMPERATURE AT  
120°F (49°C) WILL REDUCE THE RISK OF SCALDS. Some states  
or provinces require settings at specific lower temperatures. Below  
you will find listed the approximate time-to-burn relationship for  
normal adult skin. Valves for reducing point-of-use temperature by  
mixing cold and hot water are available. Also available are  
inexpensive devices that attach to faucets to limit hot water  
temperatures. Contact a licensed plumber or the local plumbing  
authority.  
HARD WATER  
Where hard water conditions exist, water softening or the threshold  
type of water treatment is recommended. This will protect the  
dishwashers, coffee urns, water boilers, water piping and other  
equipment. When water softening or water treatment is not  
practical, a comparatively easy method of periodic lime removal  
from the boiler may be employed by installing gate valves, drain  
valve and acid fill opening as shown in CLEANING AND FLUSHING  
section of this manual.  
DETAIL OF TANK FITTING USED WITH MODIFIED RECOVERY  
AND BOOSTER RECOVERY PIPING DIAGRAMS  
FIGURE 28  
32  
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A float type or an electronic probe type low water cutoff may be  
used. The manufacturer's installation instructions must be followed.  
Temperature  
Setting  
Time to Produce 2nd & 3rd  
Degree Burns on Adult Skin  
Nearly instantaneous  
About 1/2 second  
OVER: 170°F (77°C)  
160°F (71°C)  
150°F (65°C)  
140°F (60°C)  
130°F (54°C)  
120°F (49°C)  
THERMOMETERS  
About 1-1/2 seconds  
Less than 5 seconds  
About 30 seconds  
Thermometers should be obtained and field installed as shown in  
the installation diagrams.  
More than 5 minutes  
Thermometers are installed in the system as a means of detecting  
a possible liming condition in the boiler. An increase of 3°C (5°F)  
USE ANTI-SCALD VALVE(S) in the hot water system to reduce the over the normal temperature rise through the boiler is an indication  
risks of scalds at points of use such as lavatories, sinks and that lime is present. The term "temperature rise" designates the  
bathing facilities.  
difference between the boiler inlet and outlet water temperature.  
A change in water temperature in the storage tank lower than the  
Tank Temperature Control setting will cause the sensor to close  
its contacts and consequently energize the boiler.  
An increase of 3°C (5°F) above the recorded temperature rise may  
signify a liming condition in the coils or heat exchanger. Refer to  
CLEANING AND FLUSHING section of this manual for deliming  
instructions.  
If the Tank Temperature Control is out of calibration, replace it with  
a new one; do not attempt to fix this control.  
Record temperature rise at initial start-up for future reference.  
WARNING  
DRAIN VALVE (Not Supplied)  
SHOULD OVERHEATING OCCUR OR THE GAS SUPPLY FAILTO  
SHUT OFF, TURN OFF THE MANUAL GAS CONTROL VALVE TO  
THE APPLIANCE.  
A drain valve must be obtained and installed on each boiler and  
tank for draining purposes, see installation diagrams in this  
manual.  
LOW WATER CUTOFF  
CLOSED WATER SYSTEM  
A low water cutoff is a safety device which is installed in the boiler  
piping to prevent the boiler from firing in the event of inadequate  
water levels in the boiler system.  
This boiler should not be installed in a closed water system without  
taking steps to reduce excessive system pressure due to thermal  
expansion. Contact the water supplier or local plumbing inspector  
on how to control this situation.  
Where required by local code, this optional device is to be installed  
in the boiler piping at a level above that of the heat exchanger.  
33  
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ONE HW-300, HW-399, HW-420, HW-520, HW-610 OR ONE HW-670 UP-FLOW MODEL  
COMMERCIALBOILER WITH VERTICALTANK  
DANGER  
TEMPERATURE SETTING SHOULD NOT EXCEED SAFE USE  
TEMPERATURE AT FIXTURES. SEE TANK TEMPERATURE  
CONTROL WARNING ON PAGE 32. IF HIGHER PREHEAT  
TEMPERATURES ARE NECESSARY TO OBTAIN ADEQUATE  
BOOSTER OUTPUT, ADD AN ANTI-SCALD VALVE FOR HOT  
WATER SUPPLIED TO FIXTURES.  
IMPORTANT  
THE INSTALLATION OF SAFETY FLOW SWITCH AS SHOWN  
IS REQUIRED TO PROTECTTHE BOILER IN CASE OF WATER  
SERVICE INTERRUPTION OR CIRCULATOR FAILURE (A.O.  
SMITH PKG. NO. 211480).  
+
PIPING AND FITTINGS BETWEEN GATE VALVES AND  
BOILERS SHOULD BE BRASS OR BRONZE. OTHER  
PIPING SHOULD CONFORM TO LOCAL CODES.  
GATE VALVES ARE SHOWN FOR SERVICING BOILER.  
HOWEVER, LOCAL CODES SHALL GOVERN THEIR USAGE.  
*
PRESSURE RELIEF VALVE RATING SHOULD NOT  
EXCEED PRESSURE CAPACITY OF ANY COMPONENT  
IN THE SYSTEM.  
WIRING - FIGURES 17, 18,
INSTALLINACCORDANCE  
WITH ALL LOCAL CODES  
** INSTALL THERMOMETER AND PRESSURE RELIEF IN  
OPENINGS PROVIDED ON HW-520, HW-610 &  
HW-670.  
USE THIS TABLE FOR CORRECT  
PUMPAND WATER PIPE SIZE  
Minimum  
Pipe Size  
(Inches)  
1-1/4"  
1-1/2"  
1-1/2"  
B & G  
Pump  
Size  
*Armstrong  
Pump  
Model  
Number  
HW-300  
HW-399  
HW-420  
HW-520  
HW-610/670  
Size  
125  
S-25 1-1/4"  
H-32 1-1/2"  
H-32 1-1/2"  
H-32 1-1/2"  
S-35  
1-1/2" HV  
1-1/2" HV  
1-1/2" HV  
2"  
1-1/2"  
2"  
*Assumes 50 equivalent feet pf piping or less.  
FIGURE 29  
34  
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ONE HW-300, HW-399, HW-420, HW-520, HW-610 OR ONE HW-670 UP-FLOW MODEL  
COMMERCIALBOILER WITH HORIZONTALTANK  
DANGER  
TEMPERATURE SETTING SHOULD NOT EXCEED SAFE USE  
TEMPERATURE AT FIXTURES. SEE TANK TEMPERATURE  
CONTROL WARNING ON PAGE 32. IF HIGHER PREHEAT  
TEMPERATURES ARE NECESSARY TO OBTAIN ADEQUATE  
BOOSTER OUTPUT, ADD AN ANTI-SCALD VALVE FOR HOT  
WATER SUPPLIED TO FIXTURES.  
IMPORTANT  
THE INSTALLATION OF SAFETY FLOW SWI
REQUIRED TO PROTECT THE BOILER IN
SERVICE INTERRUPTION OR CIRCULATO
(A.O. SMITH PKG. NO. 211480).  
+
PIPING AND FITTINGS BETWEEN G
BOILERS SHOULD BE BRASS OR
PIPING SHOULD CONFORM TO LOCA
GATE VALVES ARE SHOWN FOR SER
HOWEVER, LOCAL CODES SHALL GOVER
*
PRESSURE RELIEF VALVE RATING SHO
PRESSURE CAPACITY OF ANY COM
SYSTEM.  
** INSTALL THERMOMETER AND PRE
OPENINGS PROVIDED ON HW-520, H
WIRING - FIGURES 17, 18, 19  
INSTALLINACCORDANCE  
WITH ALL LOCAL CODES  
USE THIS TABLE FOR CORRECT  
PUMPAND WATER PIPE SIZE  
Minimum  
Pipe Size  
(Inches)  
1-1/4"  
1-1/2"  
1-1/2"  
B & G  
Pump  
Size  
*Armstrong  
Pump  
Model  
Number  
HW-300  
HW-399  
HW-420  
HW-520  
HW-610/670  
Size  
125  
S-25 1-1/4"  
H-32 1-1/2"  
H-32 1-1/2"  
H-32 1-1/2"  
S-35  
1-1/2" HV  
1-1/2" HV  
1-1/2" HV  
2"  
1-1/2"  
2"  
*Assumes 50 equivalent feet pf piping or less.  
FIGURE 30  
35  
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TWO HW-399's, HW-420's, HW-520's, HW-610's or HW-670's UP-FLOW MODEL  
COMMERCIALBOILER WITH VERTICALTANK, CER-TEMP80  
IMPORTANT  
THE INSTALLATION OF SAFETY FLOW SWITCH AS SHOWN IS  
REQUIRED TO PROTECT THE BOILER IN CASE OF WATER SERVICE  
INTERRUPTION OR CIRCULATOR FAILURE  
(A.O. SMITH PKG. NO. 211480).  
+
PIPINGAND FITTINGS BETWEEN GATE VALVES AND BOILERS  
SHOULD BE BRASS OR BRONZE. OTHER PIPING SHOULD  
CONFORM TO LOCAL CODES.  
CING BOILER. HOWEVER,  
USAGE.  
G SHOULD NOT EXCEED  
PONENT IN THE SYSTEM.  
PRESSURE RELIEF IN  
HW-610 & HW-670.  
DANGER  
TEMPERATURE SETTING SHOULD NOT EXCEED SAFE USE TEMPERATURE AT  
FIXTURES. SEE TANK TEMPERATURE CONTROL WARNING ON PAGE 32. IF  
HIGHER PREHEAT TEMPERATURES ARE NECESSARY TO OBTAIN ADEQUATE  
BOOSTER OUTPUT, ADD ANANTI-SCALD VALVE FOR HOT WATER SUPPLIED TO  
FIXTURES.  
WIRING - FIGURES 20, 21, 22, OR 23  
HEATERS SPACED 30"APART  
INSTALLINACCORDANCE  
WITH ALL LOCAL CODES  
USE THIS TABLE FOR CORRECT  
PUMPAND WATER PIPE SIZE  
MinimumPipe Size B & G  
*Armstrong  
Pump  
Size  
Model  
Number  
HW-300  
HW-399  
HW-420  
HW-520  
HW-610/670  
(Inches)  
Pump  
Size  
2"  
2"  
2"  
A
2"  
2"  
B
1-1/2"  
1-1/2"  
1-1/2"  
1-1/2"  
1-1/2"  
S-35  
S-35  
S-35  
S-35  
2"  
2"  
2"  
2-1/2"  
2-1/2"  
S-45 2-1/2"  
*Assumes 50 equivalent feet pf piping or less.  
FIGURE 31  
36  
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TWO HW-300's, HW-399's, HW-420's, HW-520's, HW-610's OR HW-670's UP-FLOW MODEL  
COMMERCIALBOILER WITH HORIZONTAL TANK  
IMPORTANT  
THE INSTALLATION OF SAFETY FLOW SWITCHAS SHOWN IS  
REQUIRED TO PROTECT THE BOILER IN CASE OF WATER  
SERVICE INTERRUPTION OR CIRCULATOR FAILURE  
(A.O. SMITH PKG. NO.211480).  
+
GAT
HOW
*
**
WIR
DANGER  
TEMPERATURE SETTING SHOULD NOT EXCEED SAFE USE TEMPERATURE AT  
FIXTURES. SEE TANK TEMPERATURE CONTROL WARNING ON PAGE 32. IF  
HIGHER PREHEAT TEMPERATURES ARE NECESSARY TO OBTAIN ADEQUATE  
BOOSTER OUTPUT, ADD ANANTI-SCALD VALVE FOR HOT WATER SUPPLIED TO  
FIXTURES.  
USE THIS TABLE FOR CORRECT  
PUMPAND WATER PIPE SIZE  
MinimumPipe Size B & G  
*Armstrong  
Pump  
Size  
Model  
Number  
HW-300  
HW-399  
HW-420  
HW-520  
HW-610/670  
(Inches)  
Pump  
Size  
2"  
2"  
2"  
A
2"  
2"  
B
1-1/2"  
1-1/2"  
1-1/2"  
1-1/2"  
1-1/2"  
S-35  
S-35  
S-35  
S-35  
2"  
2"  
2"  
2-1/2"  
2-1/2"  
S-45 2-1/2"  
*Assumes 50 equivalent feet pf piping or less.  
FIGURE 32  
37  
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THREE HW-520's, HW-610's OR HW-670's UP-FLOW MODEL  
COMMERCIALBOILER WITH VERTICALTANK, CER-TEMP80  
WIRING - FIGURES 20, 21, 22 OR 23  
INSTALLINACCORDANCE  
WITH ALL LOCAL CODES  
DANGER  
TEMPERATURE SETTING SHOULD NOT EXCEED SAFE USE TEMPERATURE AT  
FIXTURES. SEE TANK TEMPERATURE CONTROL WARNING ON PAGE 32. IF  
HIGHER PREHEAT TEMPERATURES ARE NECESSARY TO OBTAIN ADEQUATE  
BOOSTER OUTPUT, ADD ANANTI-SCALD VALVE FOR HOT WATER SUPPLIED TO  
FIXTURES.  
IMPORTANT  
THE INSTALLATION OF SAFETY FLOW SWITCH AS SHOWN IS REQUIRED TO  
PROTECT THE BOILER IN CASE OF WATER SERVICE INTERRUPTION OR  
CIRCULATOR FAILURE  
(A.O. SMITH PKG. NO. 211480).  
+
PIPING AND FITTINGS BETWEEN GATE VALVES AND BOILERS SHOULD BE  
BRASS OR BRONZE. OTHER PIPING SHOULD CONFORM TO LOCAL CODES.  
GATE VALVESARE SHOWN FOR SERVICING BOILER. HOWEVER, LOCAL CODES  
SHALL GOVERN THEIR USAGE.  
*
PRESSURE RELIEF VALVE RATING SHOULD NOT EXCEED PRESSURE  
CAPACITY OF ANY COMPONENT IN THE SYSTEM.  
** INSTALLTHERMOMETER AND PRESSURE RELIEF IN OPENINGS PROVIDED  
ON HW-520, HW-610 & HW-670.  
USE THIS TABLE FOR CORRECT  
PUMPAND WATER PIPE SIZE  
MinimumPipe Size B & G  
*Armstrong  
Pump  
Model  
Number  
(Inches)  
Pump  
Size  
A
B
Size  
HW-520  
HW-610/670  
2-1/2"  
3"  
1-1/2"  
1-1/2"  
2"  
3" HD-3  
S-45 2-1/2"  
S-46  
*Assumes 50 equivalent feet pf piping or less.  
FIGURE 33  
38  
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THREE HW-520's, HW-610's OR HW-670's UP-FLOW MODEL  
COMMERCIALBOILER WITH HORIZONTALTANK, CER-TEMP80  
DANGER  
TEMPERATURE SETTING SHOULD NOT EXCEED SAFE USE TEMPERATURE AT  
FIXTURES. SEE TANK TEMPERATURE CONTROL WARNING ON PAGE 32. IF  
HIGHER PREHEAT TEMPERATURES ARE NECESSARY TO OBTAIN ADEQUATE  
BOOSTER OUTPUT, ADD ANANTI-SCALD VALVE FOR HOT WATER SUPPLIED TO  
FIXTURES.  
IMPORTANT  
THE INSTALLATION OF SAFETY FLOW SWITCH AS SHOWN IS REQUIRED TO  
PROTECT THE BOILER IN CASE OF WATER SERVICE INTERRUPTION OR  
CIRCULATOR FAILURE  
(A.O. SMITH PKG. NO. 211480).  
+
PIPING AND FITTINGS BETWEEN GATE VALVES AND BOILERS SHOULD BE  
BRASS OR BRONZE. OTHER PIPING SHOULD CONFORM TO LOCAL CODES.  
GATE VALVESARE SHOWN FOR SERVICING BOILER. HOWEVER, LOCAL CODES  
SHALL GOVERN THEIR USAGE.  
*
PRESSURE RELIEF VALVE RATING SHOULD NOT EXCEED PRESSURE  
CAPACITY OF ANY COMPONENT IN THE SYSTEM.  
** INSTALLTHERMOMETERAND PRESSURE RELIEF IN OPENINGS PROVIDED  
ON HW-520, HW-610 & HW-670.  
PUMPAND WATER PIPE SIZE  
WIRING - FIGURES 20, 21, 22, OR 23  
MinimumPipe Size B & G  
*Armstrong  
Pump  
Model  
Number  
(Inches)  
Pump  
Size  
HEATERS SPACED 24"APART  
A
B
Size  
HW-520  
HW-610/670  
2-1/2"  
3"  
1-1/2"  
1-1/2"  
2"  
3" HD-3  
S-45 2-1/2"  
S-46  
INSTALLINACCORDANCE  
WITH ALL LOCAL CODES  
*Assumes 50 equivalent feet pf piping or less.  
FIGURE 34  
39  
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BOOSTER RECOVERYSYSTEM (PATENTED)  
TWO TEMPERATURE SYSTEM WITHOUT RECIRCULATION  
ONE HW-300, HW-399, HW-420, HW-520, HW-610 OR HW-670 UP-FLOW MODEL  
COMMERCIALBOILER WITH VERTICALTANK  
DANGER  
+
PIPING AND FITTINGS BETWEEN GATE VALVES AND BOILERS SHOULD BE  
BRASS OR BRONZE. OTHER PIPING SHOULD CONFORM TO LOCAL CODES.  
TEMPERATURE SETTING SHOULD NOT EXCEED SAFE USE TEMPERATURE AT  
FIXTURES. SEE TANK TEMPERATURE CONTROL WARNING ON PAGE 32. IF  
HIGHER PREHEAT TEMPERATURES ARE NECESSARY TO OBTAIN ADEQUATE  
BOOSTER OUTPUT,ADD ANANTI-SCALD VALVE FOR HOT WATER SUPPLIED TO  
FIXTURES.  
GATE VALVESARE SHOWN FOR SERVICING BOILER. HOWEVER, LOCAL CODES  
SHALL GOVERN THEIR USAGE.  
*
PRESSURE RELIEF VALVE RATING SHOULD NOT EXCEED PRESSURE  
CAPACITY OF ANY COMPONENT IN THE SYSTEM.  
IMPORTANT  
THE INSTALLATION OF SAFETY FLOW SWITCH AS SHOWN IS REQUIRED TO  
PROTECT THE BOILER IN CASE OF WATER SERVICE INTERRUPTION OR  
CIRCULATOR FAILURE (A.O. SMITH PKG. NO. 211480).  
** INSTALLTHERMOMETERAND PRESSURE RELIEF IN OPENINGS PROVIDED  
ON HW-520, HW-610 & HW-670.  
WIRING - FIGURE 25 OR 27  
INSTALLINACCORDANCE  
WITH ALL LOCAL CODES  
USE THIS TABLE FOR CORRECT  
PUMPAND WATER PIPE SIZE  
Minimum  
Pipe Size  
(Inches)  
1-1/4"  
1-1/2"  
1-1/2"  
B & G  
Pump  
Size  
*Armstrong  
Pump  
Model  
Number  
HW-300  
HW-399  
HW-420  
HW-520  
HW-610/670  
Size  
125  
S-25 1-1/4"  
H-32 1-1/2"  
H-32 1-1/2"  
H-32 1-1/2"  
S-35  
1-1/2" HV  
1-1/2" HV  
1-1/2" HV  
2"  
1-1/2"  
2"  
*Assumes 50 equivalent feet pf piping or less.  
FIGURE 35  
40  
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BOOSTER RECOVERYSYSTEM (PATENTED)  
TWO TEMPERATURE SYSTEM WITHOUT RECIRCULATION  
ONE HW-300, HW-399, HW-420, HW-520, HW-610 OR HW-670 UP-FLOW MODEL  
COMMERCIAL BOILER WITH HORIZONTALTANK  
IMPORTANT  
DANGER  
THE INSTALLATION OF SAFETY FLOW SWITCH AS SHOWN IS REQUIRED TO  
TEMPERATURE SETTING SHOULD NOT EXCEED SAFE USE TEMPERATURE AT  
FIXTURES. SEE TANK TEMPERATURE CONTROL WARNING ON PAGE 32. IF  
HIGHER PREHEAT TEMPERATURES ARE NECESSARY TO OBTAIN ADEQUATE  
BOOSTER OUTPUT, ADD ANANTI-SCALD VALVE FOR HOT WATER SUPPLIED TO  
FIXTURES.  
PROTECT THE BOILER IN CASE OF WATER SERVICE INTERRUPTION OR  
CIRCULATOR FAILURE (A.O. SMITH PKG. NO. 211480).  
+
PIPING AND FITTINGS BETWEEN GATE VALVESAND BOILERS SHOULD BE  
BRASS OR BRONZE. OTHER PIPING SHOULD CONFORM TO LOCAL CODES.  
GATE VALVESARE SHOWN FOR SERVICING BOILER. HOWEVER, LOCALCODES  
SHALL GOVERN THEIR USAGE.  
SURE RELIEF VALVE RATING SHOULD NOT EXCEED PRESSURE  
CITY OF ANY COMPONENT IN THE SYSTEM.  
LL THERMOMETERAND PRESSURE RELIEF IN OPENINGS PROVIDED  
W-520 & HW-610.  
USE THIS TABLE FOR CORRECT  
PUMPAND WATER PIPE SIZE  
Minimum  
Pipe Size  
Number (Inches)  
B & G  
Pump  
Size  
*Armstrong  
Pump  
Model  
Size  
HW-300  
HW-399  
HW-420  
HW-520  
HW-610,670  
1-1/4"  
1-1/2"  
1-1/2"  
1-1/2"  
2"  
125  
S-25 1-1/4"  
H-32 1-1/2"  
H-32 1-1/2"  
H-32 1-1/2"  
S-35  
1-1/2" HV  
1-1/2" HV  
1-1/2" HV  
2"  
*Assumes 50 equivalent feet pf piping or less.  
WIRING - FIGURE 25 OR 27  
INSTALLINACCORDANCE  
WITH ALL LOCAL CODES  
PIPE SIZES "B"  
CIRCULATING LOOP TO DISHWASHER  
Type L Copper Tubing  
Allowable  
Pressure  
Drop (PSI) 25"  
(7.6m) (15m) (22.8m) (30m) (53m) (60m) (76m) (91m)  
Distance from Heater to Dishwasher (Feet./Meters)  
50"  
75"  
100" 175"  
200" 250" 300"  
10  
20  
30  
40  
50  
1/2  
1/2  
1/2  
1/2  
1/2  
3/4  
1/2  
1/2  
1/2  
1/2  
3/4  
1/2  
1/2  
1/2  
1/2  
3/4  
3/4  
1/2  
1/2  
1/2  
3/4  
3/4  
3/4  
1/2  
1/2  
3/4  
3/4  
3/4  
3/4  
3/4  
1
1
3/4  
3/4  
3/4  
3/4  
3/4  
3/4  
3/4  
3/4  
FAIRLYROUGHPIPE  
Allowable  
Distance from Heater to Dishwasher (Feet./Meters)  
Pressure  
Drop (PSI) 25"  
50" 75" 100" 175" 200" 250" 300"  
(7.6m) (15m) (22.8m) (30m) (53m) (60m) (76m) (91m)  
10  
20  
30  
40  
50  
3/4  
1/2  
1/2  
1/2  
1/2  
3/4  
3/4  
1/2  
1/2  
1/2  
3/4  
3/4  
3/4  
3/4  
1/2  
3/4  
3/4  
3/4  
3/4  
3/4  
1
1
1
1
1
3/4  
3/4  
3/4  
3/4  
3/4  
3/4  
3/4  
3/4  
3/4  
3/4  
3/4  
3/4  
3/4  
3/4  
3/4  
NOTE: Allowable pressure drop is the difference in PSI between supply  
water pressure and the 20 PSI required at the dishwasher.  
FIGURE 36  
41  
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BOOSTER RECOVERY SYSTEM (PATENTED) - TWO TEMPERATURE SYSTEM WITHOUT RECIRCULATION  
ONE HW-300, HW-399, HW-420, HW-520, HW-610 OR HW-670 UP-FLOW MODEL  
COMMERCIAL BOILER WITH HORIZONTALTANK  
+
PIPINGAND FITTINGS BETWEEN GATE VALVESAND BOILERS SHOULD BE  
BRASS OR BRONZE. OTHER PIPING SHOULD CONFORM TO LOCAL CODES.  
DANGER  
TEMPERATURE SETTING SHOULD NOT EXCEED SAFE USE TEMPERATURE AT  
FIXTURES. SEE TANK TEMPERATURE CONTROL WARNING ON PAGE 32. IF  
HIGHER PREHEAT TEMPERATURES ARE NECESSARY TO OBTAIN ADEQUATE  
BOOSTER OUTPUT, ADD ANANTI-SCALD VALVE FOR HOT WATER SUPPLIED TO  
FIXTURES.  
GATE VALVESARE SHOWN FOR SERVICING BOILER. HOWEVER, LOCAL CODES  
SHALL GOVERN THEIR USAGE.  
*
PRESSURE RELIEF VALVE RATING SHOULD NOT EXCEED PRESSURE  
CAPACITY OF ANY COMPONENT IN THE SYSTEM.  
IMPORTANT  
THE INSTALLATION OF SAFETY FLOW SWITCH AS SHOWN IS REQUIRED TO  
PROTECT THE BOILER IN CASE OF WATER SERVICE INTERRUPTION OR  
CIRCULATOR FAILURE (A.O. SMITH PKG. NO. 211480).  
** INSTALLTHERMOMETERAND PRESSURE RELIEF IN OPENINGS PROVIDED  
ON HW-520, HW-610 & HW-670.  
USE THIS TABLE FOR CORRECT  
PUMPAND WATER PIPE SIZE  
Minimum  
Pipe Size  
(Inches)  
1-1/4"  
1-1/2"  
1-1/2"  
B & G  
Pump  
Size  
*Armstrong  
Pump  
Size  
S-25 1-1/4"  
Model  
Number  
HW-300  
HW-399  
HW-420  
HW-520  
HW-610/670  
125  
WIRING - FIGURE 24 OR 26  
1-1/2" HV H-32 1-1/2"  
1-1/2" HV H-32 1-1/2"  
1-1/2" HV H-32 1-1/2"  
INSTALLINACCORDANCE  
WITH ALL LOCAL CODES  
1-1/2"  
2"  
2"  
S-35  
*Assumes 50 equivalent feet pf piping or less.  
FIGURE 37  
42  
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BOOSTER RECOVERYSYSTEM (PATENTED)  
TWO TEMPERATURE SYSTEM WITHOUT RECIRCULATION ONE HW-300, HW-399, HW-420, HW-520,HW-610 OR HW-670  
UP-FLOW MODELCOMMERCIALBOILER WITH VERTICALTANK  
DANGER  
+
PIPING AND FITTINGS BETWEEN GATE VALVES AND BOILERS SHOULD BE  
BRASS OR BRONZE. OTHER PIPING SHOULD CONFORM TO LOCAL CODES.  
TEMPERATURE SETTING SHOULD NOT EXCEED SAFE USE TEMPERATURE AT  
FIXTURES. SEE TANK TEMPERATURE CONTROL WARNING ON PAGE 32. IF  
HIGHER PREHEAT TEMPERATURES ARE NECESSARY TO OBTAIN ADEQUATE  
BOOSTER OUTPUT, ADD AN ANTI-SCALD VALVE FOR HOT WATER SUPPLIED TO  
FIXTURES.  
GATE VALVES ARE SHOWN FOR SERVICING BOILER. HOWEVER, LOCAL CODES  
SHALL GOVERN THEIR USAGE.  
*
PRESSURE RELIEF VALVE RATING SHOULD NOT EXCEED PRESSURE  
CAPACITY OF ANY COMPONENT IN THE SYSTEM.  
IMPORTANT  
THE INSTALLATION OF SAFETY FLOW SWITCH AS SHOWN IS REQUIRED TO  
PROTECT THE BOILER IN CASE OF WATER SERVICE INTERRUPTION OR  
CIRCULATOR FAILURE (A.O. SMITH PKG. NO. 211480).  
** INSTALLTHERMOMETERAND PRESSURE RELIEF IN OPENINGS PROVIDED  
ON HW-520, HW-610 & HW-670.  
FIGURE 38  
INSTRUCTIONS FOR NUMBERED CONTROLS SHOWN ABOVE -  
1
DUALTANK TEMPERATURE CONTROL  
4
FLOW REGULATING PLUG COCK  
(For Boiler Flow Rate Adjustment)  
The dual tank temperature control should be installed in the  
lower of the two 3/4" thermostat openings in the tank.  
A slight closing of this valve may be necessary to set proper  
water flow rate for 40°F temperature rise through the boiler.  
Temperature rise is observed between the boiler inlet and  
outlet thermometers.  
Left Dial -High Limit  
Adjust to 160°F with 20°F differential (minimum).  
5 FLOW REGULATING PLUG COCK  
(For Dishwasher Recirculating Loop)  
Right Dial -Tank Temperature  
Adjust to 140°F with 8°F differential (minimum).  
Close this valve just enough to divert sufficient flow into  
circulating loop that will maintain 180°F at end of loop adjacent  
to dishwasher when dishwasher is not drawing water.  
• May be adjusted slightly higher if total demand of  
180°F water requires higher tank temperature.  
2
LINE TEMPERATURE CONTROL  
6
7
WATER PRESSURE REDUCING VALVE  
Install as close to boiler as possible. Do not insulate piping or  
tee immediately adjacent to the control.  
Entering water pressure to the dishwasher must be set for 20  
psig flow pressure. Excessive flow pressure may waste rinse  
water beyond the capacity of the boiler to maintain it at 180°F  
temperature.  
Adjust dial to 185°F with 5°F differential (minimum).  
INLET/OUTLET THERMOMETERS  
• May be set slightly higher if radiant loss from piping prevents  
maintaining 180°F at dishwasher.  
See A. O. Smith deliming instructions Form 4778 when normal  
temperature rise between rinse thermometers starts to  
increase. Thermometers should be positioned near the inlet  
and outlet of the heater.  
3
BOILER LIMIT CONTROL  
(Hi Limit adjust dial 220°F with 10°F differential)  
43  
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WITH TWO VERTICAL TANKS  
DANGER  
TEMPERATURE SETTING SHOULD NOT  
EXCEED SAFE USE TEMPERATURE AT  
FIXTURES. SEE TANK TEMPERATURE  
CONTROL WARNING ON PAGE 32. IF HIGHER  
PREHEATTEMPERATURESARENECESSARYTO  
OBTAIN ADEQUATE BOOSTER OUTPUT, ADD  
AN ANTI-SCALD VALVE FOR HOT WATER  
SUPPLIED TO FIXTURES.  
WITH THREE VERTICAL TANKS  
FIGURE 39  
44  
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TWO HORIZONTALTANK INSTALLATION  
THREE HORIZONTALTANK INSTALLATION  
DANGER  
TEMPERATURE SETTING SHOULD NOT EXCEED SAFE  
USE TEMPERATURE AT FIXTURES. SEE TANK  
TEMPERATURE CONTROL WARNING ON PAGE 32. IF  
HIGHER PREHEAT TEMPERATURES ARE NECESSARY  
TO OBTAIN ADEQUATE BOOSTER OUTPUT, ADD AN  
ANTI-SCALD VALVE FOR HOT WATER SUPPLIED TO  
FIXTURES.  
FIGURE 40  
START-UP AND OPERATING INSTRUCTIONS  
4. Reset System Controller and High Limit Temperature Control  
WARNING  
to desired temperature. If unit fails to run, see Trouble-Shooting  
in this manual.  
After placing boiler into operation, the ignition system safety shutoff  
device must be tested by the following test method.  
Before operating the boiler, the entire system must be filled with  
water, purged of air and checked for leaks. Do not use Stop Leak  
or other boiler compounds. The gas piping should also be leak  
tested.  
1. Reset High Limit Temperature Control to lowest setting.  
(See figure 38, page 44).  
2. Reset System Controller to maximum setting, causing a call  
for heat and allowing unit to run until High Limit Temperature  
Control trips.  
Any safety devices including low water cutoffs used in conjunction  
with this boiler should receive periodic (every six months)  
inspection to assure proper operation. A low water cutoff device of  
the float type should be flushed every six months. All relief valves  
should be inspected and manually operated at least twice a year.  
3. Resetting the High Limit Temperature Control to a higher  
setting, unit should run.  
45  
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IMPORTANT  
IT IS RECOMMENDED THAT A QUALIFIED PERSON PERFORM  
THE INITIAL FIRING OF THE BOILER. AT THIS TIME THE USER  
SHOULD NOT HESITATE TO ASK THE INDIVIDUAL ANY  
QUESTIONS WHICH HE MAY HAVE IN REGARD TO THE  
OPERATIONAND MAINTENANCE OF THE UNIT.  
FILLING AND VENTING  
1. Fast fill system through bypass until pressure approaches  
desired system pressure. Close bypass valve and permit  
pressure to be established by the pressure reducing valve.  
FIGURE 41  
The boiler should be periodically inspected by a qualified servicer  
for continuous safe operation.  
2. Vent all high points in system to purge system of air.  
Qualified servicers should follow this procedure when the boiler’s  
burners need cleaning.  
If pressure bleeding of system is desired, install valves as shown  
in fig. 1.  
Where cast iron radiation and motorized valves are used,  
conventional system pressure and installation practices should  
be followed.  
1. Turn off the electrical power and close the main manual  
gas shutoff valve.  
•
Allow boiler parts to cool before disassembly.  
Provisions should be made to permit manual venting of radiators  
or convectors.  
2. Remove main burner manifold assembly from boiler.  
•
Refer to parts list supplied with this manual for  
disassembly aid.  
PRECAUTIONS  
If the unit is exposed to the following, do not operate boiler until all  
corrective steps have been made by a qualified serviceman:  
3. Remove any loose foreign material such as dust or lint  
with a vacuum. Check all ports, orifices, and air openings  
for blockage. Dislodge any foreign material causing  
blockage. Remove any soot or carbon deposits with a rag  
making sure to remove any lint left on burner by vacuuming  
again.  
1. Flooding to level of burner or controls or higher.  
2. Exposure to fire.  
3. If damaged.  
4. Firing without water.  
5. Sooting  
4. Reinstall the burner manifold assembly on boiler.  
5. Restore electrical power and gas supply to boiler.  
CAUTION  
SHOULD OVERHEATING OCCUR OR THE GAS SUPPLY FAILTO  
SHUT OFF, DO NOT TURN OFF OR DISCONNECT THE  
ELECTRICAL SUPPLYTO THE PUMP. INSTEAD, SHUTOFF THE  
GAS SUPPLYATALOCATION EXTERNALTO THE APPLIANCE.  
•
Put the boiler back in operation by following the lighting  
instructions in this manual or on the lighting and  
operating label on the boiler.  
PILOT AND MAIN BURNER  
•
Check for gas leaks and proper boiler and vent  
operation.  
To maintain safe operation and the greatest efficiency from the  
boiler, check the pilot and the main burner once every six months  
for proper flame characteristics.  
2. PILOT BURNER - ELECTRONIC IGNITION  
To establish pilot flame without main burner operation, it will  
be necessary to perform the following steps:  
1. MAIN BURNER  
The main burner, fig. 41, should display the following  
characteristics:  
Servicing of the pilot burner (every six months) includes keeping  
pilot shield (not shown) free of lint, cleaning the burner head,  
the primary air opening and the orifice of the pilot burner,  
fig. 42.  
•
•
Provide complete combustion of gas.  
Cause rapid ignition and carryover of flame across entire  
burner.  
1. Open fused disconnect switch or shut off electrical power  
to the boiler.  
•
•
Give reasonably quiet operation during ignition, burning  
and extinction.  
2. Turn the gas valve control knob counterclockwise to the  
“PILOT” position.  
Cause no excessive lifting of flame from burner ports.  
3. Close fused disconnect switch to restore electrical power  
to the boiler.  
If the proceeding burner characteristics are not evident, check for  
accumulation of lint or other foreign material that restricts or blocks  
the air openings to the burner or boiler.  
The pilot will now ignite provided the combination gas  
valve knob is set at “PILOT” and the system is calling for  
Also check for good flow of combustion and ventilating air to the  
unit. Maintain a clear area around the boiler at all times.  
heat.  
(Continued on Page49)  
46  
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LIGHTING AND OPERATING INSTRUCTIONS (NATURAL AND PROPANE GAS WITH I.I.D.)  
FOR YOUR SAFETY READ BEFORE OPERATING  
WARNING: IF YOU DO NOT FOLLOW THESE INSTRUCTIONS  
EXACTLY. A FIRE OR EXPLOSION MAY RESULT CAUSING PROPERTY  
DAMAGE, PERSONAL INJURY OR LOSS OF LIFE.  
WHAT TO DO IFYOU SMELLGAS  
WARNING:HOTWATERCANPRODUCE3rdDEGREE  
BURNS IN 6 SECONDSAT 140° F. (60° C).  
•
•
DO NOT TRY TO LIGHT ANY APPLIANCE.  
DO NOT TOUCH ANY ELECTRIC SWITCH;  
DO NOT USE ANY PHONE IN YOUR BUILDING.  
IMMEDIATELY CALL YOUR GAS SUPPLIER FROM A  
NEIGHBOR’S PHONE. FOLLOW THE GAS SUPPLIER’S  
INSTRUCTIONS.  
IN CASE OF POWER FAILURE DO NOT ATTEMPT TO  
OPERATE APPLIANCE. IMPROPER INSTALLATION,  
ADJUSTMENT,ALTERATION, SERVICE OR MAINTENANCE  
CAN CAUSE PROPERTY DAMAGE, PERSONAL INJURY OR  
LOSS OF LIFE. REFER TO THE USER'S INFORMATION  
MANUAL PROVIDED WITH THIS APPLIANCE.  
INSTALLATIONAND SERVICE MUST BE PERFORMED BYA  
QUALIFIED INSTALLER, SERVICE AGENCY OR THE GAS  
SUPPLIER.  
•
•
IF YOU CANNOT REACH YOUR GAS SUPPLIER, CALL  
THE FIRE DEPARTMENT.  
C. USE ONLY YOUR HAND TO PUSH IN OR TURN THE GAS  
CONTROL KNOB. NEVER USE TOOLS. IF THE KNOB WILL  
NOT PUSH IN OR TURN BY HAND, DON’T TRYTO REPAIR IT.  
CALL A QUALIFIED SERVICE TECHNICIAN. FORCE OR  
ATTEMPTED REPAIR MAY RESULT IN A FIRE OR  
EXPLOSION.  
D. DO NOT USE THISAPPLIANCE IFANY PART HAS BEEN UN-  
DER WATER. IMMEDIATELY CALL A QUALIFIED  
SERVICE TECHNICIAN TO INSPECT THE APPLIANCE AND  
TO REPLACEANY PART OF THE CONTROL SYSTEM AND  
ANY GAS CONTROLWHICH HAS BEEN UNDER WATER.  
A. THIS APPLIANCE IS EQUIPPED WITH AN IGNITION DEVICE  
WHICHAUTOMATICALLY LIGHTS THE PILOT. DO NOT TRY  
TO LIGHT THE PILOT BY HAND.  
B. BEFOREOPERATING:SMELLALLAROUNDTHEAPPLIANCE  
AREA FOR GAS. BE SURE TO SMELL NEXT TO THE FLOOR  
BECAUSE SOME GAS IS HEAVIER THAN AIR AND WILL  
SETTLE ON THE FLOOR.  
ROBERTSHAW® GAS CONTROL  
® Registered trademark of Robertshaw-Fulton Controls Company  
LIGHTING INSTRUCTIONS  
7. TURN TOP KNOB OF GAS CONTROL COUNTER-  
CLOCKWISE TO "ON" POSITION, (FIG. B). OPEN  
FIRING AND PILOT MANUAL VALVES, COUNTER-  
CLOCKWISE  
8. TURN ON ALL ELECTRIC POWER TO THE APPLIANCE.  
9. SET SYSTEM TEMPERATURE CONTROLLER TO DESIRED  
SETTING.  
10. WHEN CONTROLLER CALLS FOR HEAT, THE CIRCULAT  
ING PUMPWILLOPERATEAND THE PILOT BURNER WILL  
BESPARKIGNITED. GASCONTROLWILLOPENANDMAIN  
BURNER WILL THEN IGNITE. NOTE: IF PILOT FAILS TO  
IGNITE, TURN OFF APPLIANCE AND CONSULT YOUR  
"INSTALLATION AND USERS MANUAL" FOR ADJUST  
MENTS AND TROUBLESHOOTING.  
1.  
STOP! READ THE SAFETYINFORMATIONABOVE.  
2. MAKE SURE BOILER AND SYSTEM ARE FILLED WITH  
WATER AND ALL AIR HAS BEEN EXPELLED FROM  
APPLIANCE.  
3. TURN OFF ELECTRIC POWER TO THE APPLIANCE. SET  
SYSTEM TEMPERATURE CONTROLLER TO LOWEST  
SETTING. PURGE ALL GAS LINES OF AIR.  
.
4. DO NOT ATTEMPT TO LIGHT THE PILOT BYHAND.  
5. REFER TO DIAGRAMS ABOVE. TURN TOP KNOB OF  
GAS CONTROL CLOCKWISE  
(FIG. A). CLOSE FIRING AND PILOT MANUAL VALVES,  
CLOCKWISE  
TO "OFF" POSITION,  
.
6. WAIT FIVE (5) MINUTES TO CLEAR OUTANY GAS. THEN  
SMELL FOR GAS, INCLUDING NEAR THE FLOOR. IF YOU  
SMELL GAS,  
STOP! FOLLOW "B" IN THE SAFETY  
11. IF THEAPPLIANCE WILL NOT OPERATE, FOLLOW THE  
INSTRUCTIONS "TO TURN OFF GAS TO APPLIANCE" AND  
CALL YOUR SERVICE TECHNICIAN OR GAS SUPPLIER.  
INFORMATION ABOVE ON THIS LABEL. IF YOU DO NOT  
SMELL GAS, GO THE NEXT STEP.  
TO TURN OFF GAS TO APPLIANCE  
A. SET THE SYSTEM CONTROLLER TO THE LOWEST  
SETTING.  
B. TURN OFF ELECTRICAL POWER TO APPLIANCE.  
C. TURN TOP KNOB OF GAS CONTROL CLOCKWISE  
"OFF" POSITION, (FIG. A). CLOSE FIRING AND PILOT  
MANUAL VALVES, CLOCKWISE  
TO  
.
211686-000 Rev.00  
47  
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LIGHTING AND OPERATING INSTRUCTIONS PROPANE (LP) STANDING PILOT MODELS  
FOR YOUR SAFETY READ BEFORE LIGHTING  
WARNING: IF YOU DO NOT FOLLOW THESE INSTRUCTIONS  
EXACTLY. A FIRE OR EXPLOSION MAY RESULT CAUSING PROPERTY  
DAMAGE, PERSONAL INJURY OR LOSS OF LIFE.  
WHAT TO DO IF YOU SMELL GAS  
WARNING: HOT WATER CAN PRODUCE 3rd DEGREE  
BURNS IN 6 SECONDS AT 140° F. (60° C).  
•
•
DO NOT TRY TO LIGHT ANY APPLIANCE.  
DO NOT TOUCH ANY ELECTRIC SWITCH; DO NOT USE  
ANY PHONE IN YOUR BUILDING.  
IN CASE OF POWER FAILURE DO NOT ATTEMPT TO OPERATE  
APPLIANCE. IMPROPER INSTALLATION, ADJUSTMENT,  
ALTERATION, SERVICE OR MAINTENANCE CAN CAUSE  
PROPERTY DAMAGE, PERSONAL INJURY OR LOSS OF LIFE.  
REFER TO THE USER'S INFORMATION MANUAL PROVIDED WITH  
THIS APPLIANCE. INSTALLATION AND SERVICE MUST BE  
PERFORMED BY A QUALIFIED INSTALLER, SERVICE AGENCY  
OR THE GAS SUPPLIER.  
•
•
IMMEDIATELY CALL YOUR GAS SUPPLIER FROM A  
NEIGHBOR’S PHONE. FOLLOW THE GAS SUPPLIER’S  
INSTRUCTIONS.  
IF YOU CANNOT REACH YOUR GAS SUPPLIER, CALL  
THE FIRE DEPARTMENT.  
C. USE ONLY YOUR HAND TO PUSH IN OR TURN THE GAS CONTROL  
KNOB. NEVER USE TOOLS. IF THE KNOB WILL NOT PUSH IN OR  
TURN BY HAND, DON’T TRY TO REPAIR IT. CALL A QUALIFIED  
SERVICE TECHNICIAN. FORCE OR ATTEMPTED REPAIR MAY  
RESULT IN A FIRE OR EXPLOSION.  
A. THISAPPLIANCE IS EQUIPPED WITHA STANDING PILOT WHICH  
MUST BE LIGHTED BY THE PUSH BUTTON IGNITER. WHEN  
LIGHTING THE PILOT, FOLLOW THESE INSTRUCTIONS  
EXACTLY.  
D. DO NOT USE THIS APPLIANCE IF ANY PART HAS BEEN  
B. BEFORE LIGHTING: SMELL ALL AROUND THE APPLIANCE AREA  
FOR GAS. BE SURE TO SMELL NEXT TO THE FLOOR BECAUSE  
SOME GAS IS HEAVIER THAN AIR AND WILL SETTLE ON THE  
FLOOR.  
UNDER WATER. IMMEDIATELY CALL  
A
QUALIFIED  
SERVICE TECHNICIAN TO INSPECT THE APPLIANCE AND TO  
REPLACEANY PART OF THE CONTROL SYSTEM AND ANY GAS  
CONTROLWHICH HAS BEEN UNDER WATER.  
ROBERTSHAW® GAS CONTROL  
® Registered trademark of Robertshaw-Fulton Controls Company  
LIGHTING INSTRUCTIONS  
1.  
STOP! READ THE SAFETY INFORMATION ABOVE .  
OR UNTIL PILOT WILL CONTINUE TO STAY LIT WHEN KNOB IS  
RELEASED.  
IF THE KNOB DOES NOT POP UP WHEN RELEASED, STOP AND  
IMMEDIATELY CALL YOUR SERVICE TECHNICIAN OR GAS  
SUPPLIER.  
IF THE PILOT WILLNOT STAY LITAFTER SEVERAL TRIES, TURN  
THE GAS CONTROL KNOB TO "OFF" AND CALL YOUR SERVICE  
TECHNICIAN OR GAS SUPPLIER.  
2. MAKE SURE BOILER AND SYSTEM ARE FILLED WITH WATER  
AND ALL AIR HAS BEEN EXPELLED FROM APPLIANCE.  
3. TURN OFF ELECTRIC POWER TO THE APPLIANCE. SET SYSTEM  
TEMPERATURE CONTROLLER TO LOWEST SETTING. PURGE  
ALL GAS LINES OF AIR.  
•
•
4. REFER TO DIAGRAMS ABOVE. TURN TOP KNOB OF GAS  
CONTROL CLOCKWISE  
TO "OFF" POSITION, (FIG. A). CLOSE  
11. OBSERVE PILOT THROUGH PEEP HOLE. ADJUST PILOT FLAME  
TO HEIGHT OF APPROXIMATELY 3/8" TO 1/2" (9 TO 13mm) BY  
MEANS OF PILOT GAS REGULATOR.  
12. TURN TOP KNOB OF GAS CONTROL COUNTERCLOCKWISE TO  
"ON" POSITION. (FIG. B)  
FIRING AND PILOT MANUAL VALVES, CLOCKWISE  
.
5. WAIT FIVE (5) MINUTES TO CLEAR OUT ANYGAS. THEN SMELL  
FOR GAS, INCLUDING NEAR THE FLOOR. IF YOU SMELL GAS,  
STOP! FOLLOW "B" IN THE SAFETYINFORMATIONABOVE  
13. TURN ON ELECTRIC POWERAND SET SYSTEM TEMPERATURE  
CONTROLLER TO DESIRED OPERATING TEMPERATURE. WHEN  
CONTROLLER CALLS FOR HEAT, THE CIRCULATOR WILL  
OPERATE. GAS VALVE  
ON THIS LABEL.  
GO TO THE NEXT STEP.  
6. PILOT CAN BE VIEWED THROUGH THE PILOT PEEP HOLE. SEE  
ILLUSTRATION 1.  
7. OPEN FIRING AND PILOT MANUAL VALVES, COUNTER-  
IF YOU DO NOT SMELL GAS,  
WILL OPEN AND MAIN  
BURNER WILL THEN  
IGNITE.  
CLOCKWISE  
.
8. TURN TOP KNOB OF GAS CONTROL COUNTERCLOCKWISE  
TO "PILOT" POSITION. (FIG. C)  
14. IF THE APPLIANCE WILL  
NOT OPERATE, FOLLOW  
9. PUSH AND HOLD TOP KNOB DOWN, THIS ALLOWS GAS TO  
FLOW TO PILOT.  
THE INSTRUCTIONS "TO  
TURN OFF GAS APPL-  
10. DEPRESS PUSH BUTTON IGNITER, WHICH CAUSES SPARK TO  
JUMP ACROSS ELECTRODE, IGNITING PILOT. CONTINUE TO  
HOLD DOWN TOP KNOB FOR APPROXIMATELY 30 SECONDS  
IANCE" AND CALL YOUR  
SERVICE TECHNICIAN OR  
GAS SUPPLIER.  
ILLUSTRATION 1  
TO TURN OFF GAS TO APPLIANCE  
POSITION, (FIG. A). SEE ABOVE.  
D. TURN FIRINGAND PILOT MANUAL VALVES CLOCKWISE  
CLOSE POSITION.  
A. SET THE SYSTEM CONTROLLER TO THE LOWEST SETTING.  
B. TURN OFF ELECTRICAL POWER TO APPLIANCE.  
TO  
C. TURN TOP KNOB OF GAS CONTROL CLOCKWISE  
TO "OFF"  
211688-000 Rev.00  
48  
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(Continued from Page 46)  
4. Adjust pilot flame.  
•
The pilot flame should envelop 3/8 to 1/2 inch of the tip of the  
thermocouple. Remove pilot adjustment cover screw,  
fig. 43b. Turn inner adjustment screw or pilot adjusting valve  
clockwise to decrease, or counterclockwise to increase pilot  
flame. Be sure to replace cover screw on combination gas  
valve after adjustment to prevent possible gas leakage.  
To adjust the pilot flame, remove the cap screw from the  
pilot adjusting valve and turn to deliver a sufficient flame  
at the pilot burner to cover 3/8" to 1/2" (10-12mm) of the  
sensing probe tip. See fig. 42.  
FIGURE 42  
FIGURE 43B  
If the pilot burner ignites but the main burner fails to light, check for  
gas flow to the main burner.  
2. Clogged pilot burner orifice.  
•
Clean or replace orifice. A clogged orifice will restrict gas  
flow and result in low thermocouple output.  
Check for good terminal connection at the sensing probe at the  
pilot burner assembly.  
3. Incorrect orifice.  
Check for electrical power to the valve. If electrical power and gas  
are present at the valve and the valve does not open when system  
calls for heat, replace valve.  
•
Replace. Orifice size is stamped on the wrench flats.  
4. Clogged primary air opening.  
3. PILOT BURNER - NON-I.I.D. MODELS  
•
Restricted air passages will soften the pilot flame and result  
in poor thermocouple flame impingement.  
Servicing of the pilot burner (every six months) includes keeping  
pilot shield free of lint, cleaning the burner head, the primary air  
opening and the orifice pilot burner, fig. 43a.  
CLOSED CIRCUIT TEST  
To ensure maximum millivolt output, the pilot burner flame should  
envelop 3/8 to 1/2 inch of the thermocouple tip in fig. 43a. The  
electrical output of the thermocouple will be affected by:  
1. Attach the leads from a millivolt meter to the thermocouple and  
junction block as shown in fig. 43c.  
FIGURE 43C  
• A satisfactory thermocouple will produce a reading of above  
14 to 18 millivolts.  
2. Transfer the lead on the junction block to other terminal,  
figure 43d.  
PIEZO PILOT IGNITOR  
FIGURE 43A  
• A satisfactory voltage supply through the protector switch  
will result in a reading of 8 to 14 millivolts.  
1. Low gas pressure  
• If a reading of less than 8 millivolts is obtained, the junction  
block connections and the protector switch leads must be  
checked.  
• Adjust pilot flame by means of the pilot gas adjustment  
located in the gas valve.  
49  
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PROTECTOR SWITCH CONTINUITY TEST  
Do not depress the protector switch reset button prior to testing.  
The leads from the switch are removed from the thermocouple  
function block and attached to the leads from a test flashlight.  
The model N22T test kit (combination flashlight and continuity  
tester) is manufactured by the RAY-O-Vac Company, Madison, WI  
and available through local suppliers.  
With the flashlight turned on, the lamp should light. If the lamp  
lights, the protector switch circuit is closed and in proper working  
order. If the lamp does not light, the reasons could be:  
1. Protector switch contacts open.  
FIGURE 43D  
•
Depress reset button on switch (switch cannot be reset until  
water temperature in the boiler coils drop below 200°F). Lamp  
should light.  
The purpose of checking the current ahead and after the protector  
switch is to measure the millivolt drop across the contacts. This  
drop should be between 4 and 6 millivolts.  
2. Defective protector switch or bad leads.  
FIGURE 44  
50  
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IMPORTANT  
• If lamp does not light when reset button is depressed, attach  
the test flashlight leads to the protector switch terminals. If  
lamp does not light, switch is defective and must be replaced.  
UNDER NO CIRCUMSTANCES SHOULD THE GAS INPUT  
EXCEED THE INPUT SHOWN ON THE BOILER MODEL AND  
RATING PLATE. OVERFIRING COULD RESULT IN DAMAGE OR  
SOOTING OF THE BOILER. Minor variances from input on rating  
plate can be corrected by adjustment of gas pressure regulators  
described in GAS PRESSURE REGULATORS section of this  
manual.  
• If lamp does light, the leads are bad and must be repaired or  
replaced.  
CHECKING AND ADJUSTING THE INPUT  
1. Follow steps 1 thru 6 of the OPERATING INSTRUCTIONS.  
The inlet gas pressure must not exceed or be less than the values  
shown on rating plate.  
2. Attach a pressure gauge or a manometer to the manifold  
pressure tapping and refer to table 8 for correct manifold  
pressure.  
CONTROL SETTINGS  
MODEL HW-300, HW-399, HW-420, HW-520, HW-610 & HW-670  
3. Follow steps 7 thru 11 of the OPERATING INSTRUCTIONS.  
The high limit is a safety device wired in series with the ignition  
system. Set the high limit control to approximately 100F above the  
maximum designed system temperature. If the boiler outlet water  
temperature should exceed the high limit setting, the main gas  
valve will close but the circulator will continue to operate. Maximum  
adjustable setting is 1150C (239°F) cut-out with a 30C (50F) to 250C  
(450F) adjustable differential, fig. 45.  
4. Use this formula to “clock” the meter. Be sure that other gas  
consuming appliances are not ON during this interval.  
3600 x H = Btuh  
T
Btuh = The approximate actual input rate.  
T =  
Time in seconds to burn one cubic foot of gas.  
H =  
Heating value of the fuel gas in Btu per cubic foot of  
gas.  
EXAMPLE:  
T = 9.0 seconds/ft3  
H = 1050 Btu/ft3(natural gas)  
Btuh = ?  
FIGURE 45  
Gas flow through meter:  
ELECTRONIC INTERMITTENT PILOT  
IGNITION CONTROL  
3600 x 1050 = 420,000 Btuh  
9.0  
The solid state ignition control, fig. 46, ignites the pilot burner gas  
by creating a spark at the pilot assembly. Pilot gas is ignited and  
burns during each running cycle. The main burner and pilot gases  
are cut off during the “OFF” cycle. Pilot gas ignition is proven by the  
pilot sensor. Main burner ignition will not occur if the pilot sensor  
does not first sense pilot ignition.  
Small changes in the input rate may be made by adjusting the  
manifold pressure, see GAS PRESSURE REGULATORS. Under  
no circumstances should you exceed the maximum input rate for  
the boiler given in table 2.  
5. Repeat steps 1 thru 6 of the OPERATING INSTRUCTIONS.  
On models with the igniter control a spark continues to operate for  
15 seconds. If pilot ignition fails, there is a 5 minute wait and retry  
or unit must be manually reset.  
6. Remove the pressure gauge or manometer from the manifold  
pressure tapping. Replace the screw-in plug in the manifold  
pressure tap.  
This control is non-adjustable and has no serviceable parts. The  
removal of its cover voids the control warranty and may damage  
the electronic circuit.  
7. Repeat steps 7 thru 11 of the OPERATING INSTRUCTIONS.  
The boiler will resume normal operation.  
When the boiler is operating at full capacity, or full gas input, it  
should consume 1 cu. ft. of gas in approximately the time  
indicated in table 10.  
TABLE 10  
CONSUMPTION RATE  
(Refer to Operating at Full Input or Full Capacity)  
TIME TO CONSUME 1 CU. FT.  
Heating  
Value  
OF GAS (SECONDS)  
HWB/ HWB/ HWB/  
Type  
Gas  
HWB/  
HWB/  
HWB/  
Btu/Ft.^3 HW-300 HW-399 HW-420 HW-520 HW-610 HW-670  
Natural  
1050  
12.6  
9.5  
9.0  
7.3  
6.2  
5.7  
Propane  
2500  
30.0  
22.6  
21.4  
17.3  
14.8  
13.4  
FIGURE 46  
51  
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The input reduction is primarily achieved by reducing the size of  
the main burner orifices. To do this, the main burner orifices require  
replacement with orifices sized for the particular installation  
elevation. When ordering, be sure to state the model number and  
the altitude of the location where the boiler is being installed.  
NORMAL OPERATING SEQUENCE WITH INTERMITTENT  
IGNITION CONTROLS (I.I.D.)  
1. System control calls for boiler operation.  
2. Spark begins at pilot burner.  
Upon field deration of the boiler, adjustment to the gas pressure  
regulator is required. See CHECKING AND ADJUSTING THE  
INPUT in this manual for inlet and manifold pressure requirements.  
Also, due to the input rating reduction required at high altitudes,  
the output rating of the appliance is also reduced and should be  
compensated for in the sizing of the equipment for applications.  
3. Pilot gas control valve is energized. Gas flows to pilot burner.  
4. Pilot burner gas ignites. The sensing probe on the pilot burner  
senses the presence of the pilot flame. The spark stops after  
a few seconds.  
NOTE: If the pilot gas isn’t present or doesn’t ignite after  
15 seconds, the spark and pilot gas will stop, wait 5  
minutes, and retry or unit must be manually reset..  
THERMAL BALANCER  
Figure 47 shows the internal wiring of the thermal balancer. The  
device may be tested after disconnecting the four leads from their  
respective terminals on the unit.  
5. Main gas control valve is energized and main burner gas  
ignites.  
1. Apply a test light to the yellow and red leads.  
NOTE: If gas interruption occurs during boiler operation, the  
sensing probe will detect flame failure and within  
.8 seconds de-energize the main and pilot burner gas  
control valves. The operation of the control will revert  
back to step 2 in the foregoing.  
•
The lamp should light as the contact in this circuit is  
normally closed when the resistor is cool.  
2. Apply a light to the black and yellow leads.  
•
The lamp should not light as the contact in this circuit is  
normally open when the resistor is cool.  
6. System control stops boiler operation. Main and pilot burners  
are extinguished.  
3. Remove the test light.  
4. Apply 120 volts to the white and red leads which power the  
1900 ohm resistor. After a warming period the contacts of the  
thermal balancer should operate.  
HIGHALTITUDE INSTALLATIONS  
INCANADA  
5. Remove the test light.  
Acceptance of these models for use at altitudes above 2000 feet  
(600 m) is based on field test of the individual installation by the  
provincial/state authority having jurisdiction.  
6. Apply the test light as described in steps 1 and 2.  
While the resistor is still warm the lamp indications should be  
the opposite as described previously.  
IN THE U.S.A.  
WARNING  
INSTALLATIONS ABOVE 2000 FEET REQUIRE REPLACEMENT  
OF THE BURNER ORIFICES IN ACCORDANCE WITH SECTION  
8.1.2 OF THE NATIONALFUELGAS CODE (ANSI Z223.1). FAILURE  
TO REPLACE THE ORIFICES WILL RESULT IN IMPROPER AND  
INEFFICIENT OPERATION OF THE APPLIANCE RESULTING IN  
THE PRODUCTION OF INCREASED LEVELS OF CARBON  
MONOXIDE GAS IN EXCESS OF SAFE LIMITS WHICH COULD  
RESULT IN SERIOUS PERSONAL INJURY OR DEATH.  
FIGURE 47  
COIL HIGH LIMIT CONTROL  
(PROTECTOR SWITCH)  
For specific orifice requirements, please refer to the appropriate  
section of the National Fuel Gas Code ANSI Z223.1 or  
CGA 2.17-M91.  
This boiler is equipped with a manual reset protector switch, located  
under the small cover on the side of the jacket, fig. 48. This device  
provides positive shutdown of the heater in the event of boiler or  
system malfunction. Should the surface temperature of the copper  
tubing heat exchanger reach 120°C (250°F), the protector switch  
will activate, the gas valve will close, the pilot and main burners will  
be extinguished. If the protector switch should shut off unit, check  
the following conditions:  
You should contact your gas supplier for any specific changes  
which may be required in your area.  
Ratings specified by manufacturers for most boilers apply for  
elevations up to 2000 feet (600 m). For elevations above 2000 feet  
(600 m) ratings must be reduced by a rate of 4% for each 1000 feet  
(300 m) above sea level.  
•
•
•
•
No water in boiler.  
Restricted water flow through the boiler.  
Improper wiring (boiler firing without circulator operating).  
Pump failure.  
Example: If a boiler is rated at 610,000 Btu/hr. at sea level, to operate  
the boiler at 5000 feet (1500 m) it must be derated by 20% (4% x 5)  
to a new rating of 488,000 Btu/hr.  
After correcting failure condition remove the protector switch cover  
and push the reset button. The protector switch may be reset after  
the coil surface temperature cools to .6°C (1°F).  
A. O. Smith does build some models specifically for high altitude  
service. Please check the rating plate before making changes.  
52  
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For proper performance mount the switch in a section of pipe  
where there is a straight run of at least 5 pipe diameters on each  
side of the flow switch (i.e. do not locate adjacent to valves, elbows,  
orifices, etc.).  
The flow switch shall be mounted in a standard 1-1/2" x 1-1/2" x 1"  
tee for a 1-1/2" pipe application. For larger pipe sizes use a  
reducing tee in order to keep the switch as close to the pipe as  
possible. Install the flow switch in the branch (top) opening of the  
reducing tee and provide adequate paddle length in the flow stream.  
For example in a 2" pipe installation use a 2" x 2" x 1" reducing tee.  
For 2", or 3" pipe use paddle segments as supplied. For other  
pipe sizes (i.e. 1-1/4", 1-1/2" and 2-1/2") trim the paddle to the  
proper pipe size, see fig. 49. If a standard tee is used, install a face  
or hex bushing in the top opening. The paddle must be adjusted  
or trimmed to the size of the pipe in which it will be installed.  
PROTECTOR SWITCH  
FIGURE 48  
PRESSURE REDUCING VALVE  
The screen in the pressure reducing valve may require occasional  
cleaning due to foreign material in the water supply. This will  
restrict the flow and could reduce the effectiveness of purging and  
prolong filling time. To inspect the screen, close the main water  
supply valve ahead of the pressure reducing valve and remove the  
screen for cleaning, see fig’s. 1 and 2.  
CAUTION  
Any part of the paddle must not touch the pipe or any restrictions in  
the pipe. Screw the flow switch in position so the flat of the paddle  
is at right angles to the flow. The arrow on the side case must point  
in the direction of the flow.  
TABLE 11 - SAFETYFLOW SWITCH  
SAFETY FLOW SWITCH  
The safety flow switch is a safety device which must be installed at  
the water outlet of the unit to prevent main burner operation in the  
event of inadequate water flow through the unit, see fig’s. 10 through  
12 and 17 through 27.  
Minimum Pipe Rate  
Contacts Closed  
(Flow)  
Contacts Open  
(No Flow)  
Model  
Number  
GPM  
5.8  
7.5  
7.5  
13.7  
13.7  
LPS  
0.36  
0.47  
0.47  
0.86  
0.86  
GPM  
3.7  
LPS  
HWB/HW-300  
HWB/HW-399  
HWB/HW-420  
HWB/HW-520  
HWB/HW-610/670  
0.23  
0.31  
0.31  
0.60  
0.60  
5.0  
An accessory package A. O. Smith No. 211480 containing a safety  
flow switch is available for this application.  
5.0  
9.5  
9.5  
This switch may be mounted in a horizontal pipe line or a vertical  
pipe line with upward water flow. Do not install the switch where  
the water flow is downward.  
The safety flow switch may be field adjusted to obtain higher  
minimum flow rates than those shown in table 11.  
CAUTION  
Paddle must be trimmed at the dotted arc. It must not touch  
the pipe or have any restriction when installed  
FIGURE 49  
53  
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To adjust the flow rate setting:  
Thermal expansion is the normal response of water when it is  
heated. In a closed system, thermal expansion will cause the  
system pressure to build until the relief valve actuation pressure is  
equaled. Then, the relief valve will open, allowing some water to  
1. Remove the flow switch cover.  
2. For higher flow rate—turn the range adjusting screw clockwise. escape, slightly lowering the pressure.  
A properly sized expansion tank should be installed.  
3. For lower flow rate—turn the range adjusting screw  
counter-clockwise.  
ABOVE ALL, DO NOT PLUG ANY RELIEF VALVE. THIS IS NOTA  
SOLUTIONAND CAN CREATE AHAZARDOUS SITUATION.  
CAUTION  
The switch is factory set at approximately the minimum flow rate,  
see Table II. It must not be set lower than the factory setting as this  
may result in the switch failing to return at a “no flow” condition.  
REPLACEMENT PARTS  
U.S. Models  
Replacement parts may be ordered through A. O. Smith dealers,  
authorized servicers or distributors. Refer to the Yellow Pages for  
where to call or contact the A. O. Smith Water Products Company,  
5621 W. 115th Street, Alsip, IL 60803, 1-800-433-2545. When  
ordering parts be sure to state the quantity, part number and  
description of the item including the complete model and serial  
number as it appears on the product. Refer to the parts lists for  
more information.  
4. Replace the flow switch cover.  
Where units are installed in multiples, each boiler must be  
individually protected by a safety flow switch.  
SAFETYRELIEF VALVE MAINTENANCE  
Every six months the system safety relief valves should be checked  
to ensure that they are in operating condition. To check a relief  
valve, lift the lever at the end of the valve several times. The valve  
Canadian Models  
should seat properly and operate freely.  
Replacement parts may be ordered through A. O. Smith dealers,  
authorized servicers or distributors. Refer to the Yellow Pages for  
where to call or contact the A. O. Smith Enterprises, Ltd., P. O. Box  
310, 768 Erie St., Stratford, Ontario N5A 6T3, 1-800-265-8520.  
When ordering parts be sure to state the quantity, part number and  
description of the item including the complete model and serial  
number as it appears on the product. Refer to the parts lists for  
more information.  
CAUTION  
BEFORE MANUALLY OPERATINGARELIEF VALVE, MAKE SURE  
THAT A DRAIN LINE HAS BEEN ATTACHED TO THE VALVE TO  
DIRECT THE DISCHARGE TO AN OPEN DRAIN. FAILURE TO  
TAKE THIS PRECAUTION COULD MEAN CONTACT WITH  
EXTREMELY HOT WATER EXITING THE VALVE DURING THIS  
CHECK OPERATION.  
If a relief valve discharges periodically or continuously, it may be  
due to thermal expansion of water in a closed water supply system,  
or, it may be due to thermal expansion of water in a closed water  
supply system, or, it may be due to a faulty relief valve.  
QUALITY REPLACEMENT PARTS  
REMOVAL OF EXISTING BOILER FROM A COMMON VENTING SYSTEM  
Place in operation the appliance being inspected. Follow the  
lighting instructions. Adjust thermostat so appliance will operate  
continuously.  
At the time of removal of an existing boiler, the following steps shall  
be followed with each appliance remaining connected to the  
common venting system placed in operation, while the other  
appliances remaining connected to the common venting system  
are not in operation.  
Test for spillage at the draft hood relief opening after 5 minutes of  
main burner operation. Use the flame of a match or candle, or  
smoke from a cigarette, cigar or pipe.  
Seal any unused openings in the common venting system.  
After it has been determined that each appliance remaining  
connected to the common venting system properly vents when  
tested as outlined above, return doors, windows, exhaust fans,  
fireplace dampers and any other gas-burning appliance to their  
previous condition of use.  
Visually inspect the venting system for proper size and horizontal  
pitch and determine there is no blockage or restriction, leakage,  
corrosion and other deficiencies which could cause an unsafe  
condition.  
Insofar as is practical, close all building doors and windows and  
all doors between the space in which the appliances remaining  
connected to the common venting system are located and other  
spaces of the building. Turn on clothes dryers and any appliance  
not connected to the common venting system. Turn on any exhaust  
fans, such as range hoods and bathroom exhausts, so they will  
operate at maximum speed. Do not operate a summer exhaust  
fan. Close fireplace dampers.  
Any improper operation of the common venting system should be  
corrected so the installation conforms with the National Fuel Gas  
Code, ANSI Z223.1 and/or CAN/CGA B149, Installation Codes.  
When resizing any portion of the common venting system, the  
common venting system should be resized to approach the  
minimum size as determined using the appropriate tables in  
Appendix F in the National Fuel Gas Code, ANSI Z223.1 and/or  
CAN/CGA B149 Installation Codes.  
54  
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GENERAL MAINTENANCE  
More frequent inspections may be necessary depending on water  
conditions.  
These boilers are designed to give many years of efficient and  
satisfactory service when properly operated and maintained. To  
assure continued good performance, the following  
recommendations are made.  
The boiler mounted gas and electrical controls have been designed  
to give both dependable service and long life. However, malfunction  
can occur, as with any piece of equipment. It is therefore  
recommended that all components be checked periodically by a  
qualified serviceman for proper operation.  
The area around the unit should be kept clean and free from lint  
and debris. Sweeping the floor around the boiler should be done  
carefully. This will reduce the dust and dirt which may enter the  
burner and pilot air passages, causing improper combustion and  
sooting.  
RELIEF VALVE  
The safety relief valve should be opened at least twice a year to  
check its working condition. This will aid in assuring proper  
pressure relief protection. Lift the lever at the top of the valve several  
times until the valve seats properly and operate freely.  
THE FLOW OF COMBUSTION AND VENTILATION AIR TO THE  
BOILER MUST NOT BE OBSTRUCTED.  
THE BOILER AREA MUST BE KEPT CLEAR AND FREE FROM  
COMBUSTIBLE MATERIALS, GASOLINE, AND OTHER  
FLAMMABLE VAPORSAND LIQUIDS.  
DANGER  
THE WATER PASSING OUT OF THE VALVE DURING CHECKING  
OPERATION MAY BE EXTREMELY HOT. BEFORE OPERATING  
RELIEF VALVE MAKE SURE DRAIN LINE IS INSTALLED TO  
DIRECT DISCHARGE TOASAFE LOCATION SUCHASAN OPEN  
DRAIN, TOAVOID SCALDING OR WATER DAMAGE.  
Any safety devices including low water cutoffs used in conjunction  
with this boiler should receive periodic (every six months)  
inspection to assure proper operation. A low water cutoff device of  
the float type should be flushed every six months. All relief valves  
should be inspected and manually operated at least twice a year.  
More frequent inspections may be necessary depending on water  
conditions.  
WARNING  
SHOULD OVERHEATING OCCUR OR THE GAS SUPPLY FAILTO  
SHUT OFF, TURN THE MANUAL GAS CONTROL VALVE TO THE  
APPLIANCE.  
Periodic checks, at least twice a year, should be made for water  
and/or gas leaks.  
CLEANING AND FLUSHING INSTRUCTIONS  
INTERNALCONTAMINANTS  
HOT WATER SUPPLY BOILERS  
PREVENTIVE MAINTENANCE  
The hydronic system must be internally cleaned and flushed after  
a new or replacement boiler has been installed to remove  
contaminants that may have accumulated during installation. This  
is doubly important when a replacement boiler is installed into an  
existing system where Stop Leak or other boiler additives have  
been used.  
Some solids exist in most water supply systems. As the water is  
heated, these tend to drop out depositing as scale or lime. This  
scale is comparatively easy to remove if cleaned before the unit  
becomes clogged. The time between cleaning will vary depending  
upon water conditions and usage. A change of about 50F (3°C) in  
the normal temperature rise through the unit is usually an indication  
that it is time for preventive maintenance.  
Failure to clean and flush the system can produce acid  
concentrations that become corrosive, cause gases to form that  
block water circulation or lead to formation of deposits on the boiler  
surfaces, any of which could result in damage to the system and  
circulator.  
Figure 31 shows typical piping arrangement for gravity deliming of  
lime deposits.  
DELIMING  
All hot water heating systems should be completely flushed with a  
grease removing solution to assure trouble-tree operation. Pipe  
joint compounds, soldering paste, grease on tubing and pipe all  
tend to contaminate a system.  
The amount of calcium carbonate (lime) released from water is in  
direct proportion to water temperature and usage, see fig. 49. The  
higher the water temperature or water usage, the more lime  
deposits are dropped out of the water. This is the lime scale which  
forms in pipes, boilers and on cooking utensils.  
Failure to flush contaminates from a system can cause solids to  
form on the inside of boiler exchangers, create excessive amounts  
of air and other gases to block circulation, foul various system  
accessories and even deteriorate circulation seals and impellers.  
Lime accumulation not only reduces the life of the equipment but  
also reduces efficiency of the boiler and increases fuel  
consumption.  
It is recommended that after installation, the boiler and system  
when filled should include the proper percentage of cleaning  
solution related to approximate water volume of the system. Fire  
and circulate for about one hour and then flush clean with fresh  
water. Commercial grease removing solutions are available from  
your distributor.  
The usage of water softening equipment greatly reduces the  
hardness of water. However, this equipment does not always  
remove all of the hardness (lime). For this reason it is  
recommended that a regular schedule for deliming be maintained.  
55  
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The time between cleaning will vary from two to six months 9. When foaming action has stopped completely, allow 10 to  
depending upon water conditions and usage. A change of  
approximately 50F in the normal temperature rise through the boiler  
is usually an indication that scale should be removed. For long  
15 minutes for the solvent to dissolve any remaining scale in  
the unit.  
life, copper or brass is recommended for all valves, pipe and fittings 10. Open the drain cock and drain all the solvent from unit.  
used between gate valves “A” and “B” and the boiler, see fig. 51.  
11. Remove standpipe and drain hose assembly from tees. Install  
Boiler failure due to excessive lime build-up voids the warranty.  
fittings originally removed into openings. Open valve “A”  
allowing fresh water to flow through unit and out drain cock for  
three to five minutes.  
12. Close drain cock and open valve “B”. Restore electric and  
gas supply.  
Check unit for proper operation.  
FIGURE 50  
DELIMING THE HWB/HW BOILER  
FIGURE 51  
DELIMING SOLVENTS  
MINIMUM AMOUNT OF CLEANING  
A. O. Smith recommends the use of generic commercially available  
cleaning solutions to remove lime buildup from your system.  
SOLUTION REQUIRED  
Model  
Number  
Litres  
12  
19  
19  
26  
Gallons  
HWB/HW-300  
HWB/HW-399  
HWB/HW-420  
HWB/HW-520  
HWB/HW-610/670  
3
5
5
7
7
CAUTION  
Read the instructions on the label of the deliming solvent container.  
26  
REMOVING LIGHT DEPOSITS OF SCALE  
1. Shut off electric and gas supply to the unit.  
2. Close gate valves “A” and “B”, see fig.51.  
3. Open drain cock and drain unit.  
HEAVY LIME DEPOSITS  
If the solvent does not readily pass through the clogged coils or  
heat exchanger, it will be necessary to use an acid pump deliming  
kit, or contact a service agency for proper cleaning.  
A. O. Smith part no. 4930 motorized deliming pump kit, complete  
with pump, hoses, fittings, container and instructions is available  
from your dealer, distributor or the A. O. Smith Water Products  
Company.  
4. Remove pressure relief valve from outlet header assembly  
and install drain hose assembly, see fig. 51.  
5. Install standpipe in tee of inlet line, see fig. 51.  
6. Close drain cock.  
REMOVING SILICATE  
Ammonium bifluoride flakes (NH4F HF) can be used in conjunction  
7. Slowly pour required amount of deliming solvent shown below with delimer to delime and remove siliceous materials from copper  
into unit through standpipe. Direct solution into suitable coil water boilers.  
container with hose, see illustration.  
Ammonium bifluoride flakes should be purchased locally from  
8. Continue to fill until foaming action stops.  
chemical suppliers.  
56  
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—
Gas supply pressure is within the maximum and minimum operating  
ranges listed on the appliance rating plate/label.  
PRE-TROUBLESHOOTING  
Before any extensive trouble-shooting, perform the following:  
Ensure That:  
—
—
Voltage (24 vac) is supplied by transformer.  
Appliance is wired according to wiring diagram.  
—
—
Voltage (120 vac) is supplied to the appliance.  
Note: Cross wiring the 24 volt circuit of the relay will short the transformer.  
System control (tank temperature control, thermostat, etc.) is calling  
for appliance operation (call for heat).  
—
All wire terminals/connectors are firmly attached to valves, modules,  
switches, limit controls, etc.  
—
Other contacts (switches) are closed (relay, low water cutoff, flow  
switch, coil protector, pressure switch, etc.).  
—
For LP models only check for possible lockout condition of the ignition  
module.  
TROUBLESHOOTING  
CER-TEMP 80 RECOVERY SYSTEM CHECKOUT PROCEDURE  
Use this checkout for Cer-Temp 80 Recovery Systems. (For hot water supply application only)  
SYSTEM OPERATION  
Checkout Sequence  
Contact  
Incorrect  
Cause  
Remedy  
Set tank temperature  
control (thermostat)  
20°F (10°C) below  
Circulating pump  
and burner shut  
off.  
Pump and burner Tank temperature control  
Replace.  
remain on.  
(thermostat) defective.  
tank water temperature  
With thermal  
System wiring is incorrect.  
Correct wiring.  
balancer, pump off  
delay of approx-  
imately 2 minutes.  
Circulating pump Pump wired for continuous Correct wiring.  
on.  
operation.  
Burner on.  
Gas valve stuck or defective. Correct or replace valve.  
System wiring is incorrect.  
Correct wiring.  
Set tank temperature  
control (thermostat)  
20°F (10°C) above  
Circulating pump  
and burner on.  
Circulating pump High limit control set too  
on. low.  
Replace. (If problem  
proven to be at this  
control by applying  
tank water temperature.  
High limit control differential jumper to terminals.)  
too wide.  
System wiring is incorrect.  
Correct wiring.  
Coil protector switch has  
activated.  
Remove control cover,  
depress reset button.  
Gas valve or wiring  
defective.  
Check wiring. Repair or  
replace valve.  
Circulating pump Power off or system  
Check power supply  
and wiring.  
and burner off.  
wiring is incorrect.  
Tank temperature control  
(thermostat) defective.  
Replace.  
Burner on.  
System wiring is incorrect.  
Correct wiring.  
Replace.  
Boiler outlet  
temperature exceeds  
210°F (100°C).  
Circulating pump  
on.  
Circulating pump High limit control defective,  
and burner on.  
or set too high (max. should  
be set at 200°F).  
Set tank temperature  
control (thermostat)  
for desired water  
temperature.  
System maintains.  
desired water  
temperature.  
57  
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CHECKING HONEYWELL S-8600H OR S-8610M  
INTERMITTENT IGNITION CONTROLS  
NO SPARK AT PILOT BURNER  
Turn off gas supply.  
NO  
Is voltage (24 Vac) across the 24 V terminals  
on module during “Call for heat”?  
Replace ignition module.  
YES  
Is voltage (24 Vac) across the PV & MV/PV terminals on  
“call for heat”?  
YES  
NO  
NOTE: S8610M will automatically reset every 5 minutes.  
S8600H pilot valve will be de-energized if module goes into  
lockout condition. Reset system by turning electrical power off or  
by turning system controller to off or down below "call for heat".  
Wait one minute, then turn system on.  
YES  
Turn on gas supply.  
turn on power supply.  
Turn off power supply.  
Is ignition cable firmly plugged into pilot  
assembly and module?  
NO  
NO  
Securely connect cable  
and/or ground wire.  
Is ground wire firmly attached to pilot assembly and GND  
terminal on module?  
YES  
Replace pilot burner  
and/or ground wire.  
Are ignition cable and ground wire in good condition  
(not brittle, burnt or cracked)?  
YES  
Ensure ground strap is the closest metal to the igniter/sensor  
rod (electrode) to prevent the spark from shorting out to other  
metal parts (pilot screen, pilot shield, etc.).  
NO  
NO  
Carefully bend downward  
top of ground strap  
to achieve 1/8”  
Ignition cable must not touch metal surfaces or current  
carrying wires.  
spark gap.  
Is there a 1/8” gap between ground strap and electrode?  
YES  
Is the ceramic insulator surrounding the electrode  
cracked or broken?  
Replace Ignition  
Module.  
YES  
Replace pilot burner assembly.  
58  
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CHECKING HONEYWELL S8600H OR S-8610M  
INTERMITTENT IGNITION CONTROLS  
SPARK AT PILOT BURNER BUT PILOT WILL NOT LIGHT  
Ensure all manual shutoff valves are fully open; All filters are  
clean; All gas connections are gas tight; Pilot tubing is not  
damaged, obstructed or kinked; and pilot orifice is unclogged.  
Check for air in gas line, purge (bleed) line if necessary.  
YES  
NO  
NO  
Are the wires securely attached to the pilot operator on the gas  
control and to the PV & MV/PV terminals on the ignition module?  
Attach wires firmly.  
YES  
Install a pressure gauge in the pilot tubing line between the gas  
control and the pilot burner assembly. Ensure that the pilot  
adjustment screw (under cap) is adjusted to a position that will  
permit gas to flow.  
Replace gas valve.  
Is pilot gas flowing during ignition attempt?  
YES  
Turn on power supply  
Turn off power supply.  
YES  
Is ignition cable firmly plugged into pilot assembly and  
module?  
NO  
Securely connect  
cable and/or ground  
wire.  
Is ground wire firmly attached to pilot assembly and GND  
terminal on module?  
YES  
NO  
Replace pilot burner  
and/or ground wire.  
Are ignition cable and ground wire in good condition (not brittle, burnt, or cracked)?  
YES  
Ensure ground strap is the closest metal to the igniter/sensor  
rod (electrode) to prevent the spark from shorting out to  
other metal parts (pilot screen, pilot shield, etc.).  
Carefully bend down-  
wards top of ground  
strap to achieve  
NO  
Ignition cable must not touch metal surfaces or current  
carrying wires.  
1/8” spark gap.  
Is there a 1/8” gap between ground strap and electrode?  
YES  
NO  
Is ceramic insulator surrounding the electrode in good  
Replace pilot burner.  
condition (not cracked or broken)?  
YES  
NO  
Replace Ignition  
Module.  
Is there excessive draft conditions that may cause pilot  
burner ignition problems?  
YES  
Correct draft problems in a manner that would ensure  
adequate combustion and ventilation air and proper  
pilot burner performance.  
59  
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CHECKING HONEYWELL S-8600H OR S8610M  
INTERMITTENT IGNITION CONTROLS  
PILOT BURNER LIGHTS BUT MAIN BURNER DOES NOT LIGHT  
Correct the situation by consulting the  
installation or user’s manual on how to  
adjust pilot flame.  
NO  
NO  
Does the pilot flame cover 3/8” to 1/2”  
of ingniter/sensor rod?  
YES  
Replace  
ignition  
module.  
NO  
Does spark stay on for more than  
15 seconds after the pilot is “proven” (lit)?  
Is voltage (24 Vac) across terminals  
MV & MV/PV?  
YES  
Are the wires securely attached to the main  
valve operator on the gas control and to  
terminals MV & MV/PV on ignition module?  
Attach  
wires  
firmly.  
NO  
YES  
YES  
Replace main gas valve.  
Ensure the ground wire and ignition cable are  
separate from each other (prevents shorting  
out).  
NO  
Replace pilot burner  
and/or ground wire.  
Are they in good condition (not brittle, burnt or  
cracked)?  
YES  
NO  
NO  
Is the ceramic insulator surrounding the  
igniter/sensor rod in good condition  
(not broken or cracked)?  
Replace pilot burner.  
YES  
Is the igniter/sensor rod in good  
condition (not worn, corroded, sooted  
or damaged)?  
Clean rod or replace  
pilot burner if necessary.  
YES  
Replace ignition module.  
60  
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CHECKING HONEYWELL S8600H OR S-8610M  
INTERMITTENT IGNITION CONTROLS  
NO SPARK AT PILOT BURNER BUT PILOT WILL NOT LIGHT  
Turn off gas supply.  
Fix connection and/or  
NO  
Is there a good connection between terminals?  
tighten module to the  
appliance  
Is module securely attached to appliance for good ground  
connection?  
YES  
NO  
NO  
Check the circuit providing  
24 VAC.  
Is voltage (24VAC across transformer positive terminal and  
GND with "call for heat"??  
YES  
Is voltage (24VAC) across ignition module terminals 24 Volt and  
GND on "call for heater"?  
Replace ignition module.  
NOTE: (For LP models only) Pilot Valve will be de-energized if  
module goes into lockout condition. Reset system by turning  
electrical power off or by turning system controller down below  
"call for heat". Wait one minute then turn system on.  
Turn on gas supply and/  
or power supply.  
YES  
Turn off power supply.  
NO  
NO  
Securely connect cable  
and/or ground wire.  
Is high voltage cable assembly firmly plugged into module?  
Is pilot ground wire firmly attached to the pilot assembly and  
GND terminal on module?  
YES  
Replace pilot burner  
and/or ground wire.  
Are high voltage cable and ground wire in good condition (not  
brittle, burnt or cracked)?  
YES  
Make sure pilot flame spreader (hood) is the closest metal to  
the electrode to prevent the spark from shorting out to other  
metal parts (pilot screen, pilot shield, etc).  
Carefully bend down-  
wards top of ground  
strap to achieve  
NO  
NO  
High voltage cable must not touch metal surfaces or current  
carrying wires.  
1/8” spark gap.  
Is there a 7/64" spark gap between the tip (edge) of the hood  
and electrode, and is the gap located in the pilot gas stream?  
YES  
Is the ceramic insulator surrounding the electrode in good  
condition (not cracked or broken)?  
Replace Ignition Module.  
YES  
Replace Pilot Burner Assembly  
61  
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LIMITED WARRANTY  
A. O. Smith Corporation, the warrantor, extends the following LIMITED WARRANTY to the owner of this hydronic boiler.  
1. If within TEN years after initial installation of the boiler, a heat exchanger, coil or gas burner shall prove upon examination by the warrantor to be  
defective in material or workmanship, the warrantor, at his option will exchange or repair such part or portion. This term is reduced to FIVE years  
if this boiler is used for water heating purposes other than hydronic space heating.  
a. This warranty is extended to the owner for all other parts or portion during the FIRST year following initial installation of this boiler.  
b. The warranty on the repair or replacement of the part or portion will be limited to the unexpired term of the original warranty.  
3. CONDITIONS AND EXCEPTIONS  
This warranty shall apply only when the boiler is installed in accordance with local plumbing and building codes, ordinances and regulations, the  
printed instructions provided with it and good industry practices. In addition, an appropriately sized safety relief valve certified to the ASME Boiler  
and Pressure Vessel Code must have been installed and fresh, clean water used for filling and make-up purposes.  
a. This warranty shall apply only when the boiler is:  
(1) used at temperatures not exceeding the maximum setting of its operative and/or high limit control;  
(2) used at water pressure not exceeding the working pressure shown on the boiler;  
(3) used when filled with potable water, free to circulate at all times and with the heat exchanger(s) and coil(s) free of damaging scale  
deposits;  
(4) in a non-corrosive and non-contaminated atmosphere;  
(5) owned by the original purchaser;  
(6) in it's original installation location;  
(7) is sized in accordance with proper sizing techniques for commercial boilers;  
(8) bearing a rating plate which has not been altered, defaced or removed except as required by the warrantor;  
(9) fired at the factory rated input using the fuel stated on the rating plate;  
(10) maintained in accordance with the instructions printed in the manual included with the boiler;  
(11) in the United States, its territories or possessions, and Canada;  
(12) with an intermittent circulating action and with the pump and burner operating together.  
(13) in an indoor installation only.  
b. Any accident to the boiler, any misuse, abuse (including freezing) or alteration of it, any operation of it in a modified form, or any attempt to repair  
leaks in the coil or heat exchanger will void this warranty.  
4. SERVICEAND REPAIR EXPENSE  
Under this limited warranty the warrantor will provide only a replacement part. The owner is responsible for all other costs. Such costs may include  
but are not limited to:  
a. Labor charges for service, removal, repair or reinstallation of the component part;  
b. Shipping, delivery, handling, and administrative charges for forwarding the replacement part from the nearest distributor and returning the  
claimed defective part to such distributor.  
c. All cost necessary or incidental for any materials and/or permits required for installation of the replacement.  
5. LIMITATION ON IMPLIED WARRANTIES  
Implied warranties, including any warranty of merchantability imposed on the sale of this boiler under state law are limited to one (1) year duration  
for the boiler or any of its parts. Some states do not allow limitations on how long an implied warranty lasts, so the above limitation may not apply  
to you.  
6. CLAIM PROCEDURE  
Any claim under this warranty should be initiated with the dealer who sold the boiler, or with any other dealer handling the warrantor’s products. If  
this is not practicable, the owner should contact:  
U. S. Customers  
Canadian Customers  
A. O. Smith Corporation  
5621 West 115th Street  
Alsip, IL 60803  
A. O. Smith Enterprises Ltd.  
P. O. Box, 310 - 768 Erie Street  
Stratford, Ontario N5A 6T3  
Telephone: 1-800-265-8520  
Telephone: 1-800-323-2636  
a. The warrantor will only honor replacement with identical or similar parts thereof which are manufactured or distributed by the warrantor.  
b. Dealer replacements are made subject to in-warranty validation by warrantor.  
7. DISCLAIMERS  
NO OTHER EXPRESS WARRANTY HAS BEEN OR WILLBE MADE IN BEHALF OFTHE WARRANTOR WITH RESPECTTO THE MERCHANTABILITYOF  
THE BOILER ORTHE INSTALLATION, OPERATION, REPAIR OR REPLACEMENTOF THE BOILER. THE WARRANTOR SHALLNOTBE RESPONSIBLE  
FOR WATER DAMAGE, LOSS OF USE OFTHE UNIT, INCONVENIENCE, LOSS OR DAMAGETO PERSONALPROPERTY, OR OTHER CONSEQUENTIAL  
DAMAGE. THE WARRANTOR SHALL NOT BE LIABLE BY VIRTUE OF THIS WARRANTY OR OTHERWISE FOR DAMAGE TO ANY PERSONS OR  
PROPERTY, WHETHER DIRECTOR INDIRECT,AND WHETHERARISING IN CONTRACT OR TORT.  
a. Some states or provinces do not allow the exclusion or limitation of the incidental or consequential damage, so the above limitations or exclusions  
may not apply to you.  
b. This warranty gives you specific legal rights, and you may also have other rights which vary from state to state.  
Fill in the following for your own reference. Keep it. Registration is not a condition of warranty. The model and serial number are found on the  
boiler’s rating plate.  
Owner___________________________________________________________________________________________________________________  
Installation Address________________________________________________________________________________________________________  
City and State/Province _________________________________________________________Postal/Zip Code_______________________________  
Date Installed _________________________________ Model No. ___________________________  
Serial No.________________________  
Dealer’s Name ____________________________________________________________________ Phone No._______________________________  
Dealer’s Address__________________________________________________________________________________________________________  
FILL IN DATA AND KEEP FOR FUTURE REFERENCE  
62  
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REPLACEMENT PARTS  
5621 W. 115TH STREET, ALSIP, IL 60803  
PHONE: 1-800-433-2545 FAX: 1-800-433-2515  
E-MAIL: [email protected] • www.hotwater.com  
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