A.O. Smith 120 through 250 Series How to use

1
Service Handbook
PRINTED IN THE U.S.A 0510 318349-000
SERVICING SHOULD ONLY BE PERFORMED BY A QUALIFIED SERVICE AGENT.
COMMERCIAL GAS WATER HEATERS
INSTALLATION CONSIDERATIONS - PRE SERVICE
CHECKS - WATER HEATER CONSTRUCTION -
OPERATION & SERVICE - TROUBLESHOOTING
500 Tennessee Waltz Parkway
Ashland City, TN 37015
INSTALLATION CONSIDERATIONS - PRE SERVICE
CHECKS - OPERATION & SERVICE -TROUBLESHOOTING
MODEL BTR 500/A SERIES 120/121

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Servicing should only be performed by a Qualified Service Agent
INTRODUCTION............................................................3
Qualifications ...........................................................3
Service Warning........................................................3
Service Reminder .....................................................3
REQUIREMENTS...........................................................4
Instruction Manual ....................................................4
Tools Required..........................................................4
Tools Optional ...........................................................4
INSTALLATION CONSIDERATIONS .............................5
Water Piping .............................................................5
Closed Water Systems........................................5
Thermal Expansion .............................................5
Gas Pressure Requirements ....................................5
Air Requirements ......................................................6
Air Supply............................................................6
Insufficient Make-up Air, Negative Air Pressure,
and Downdrafts...................................................7
Make-up Air: Direct Communication with Out-
doors ...................................................................8
Contaminated Air ................................................9
Clearances (Water Heater).......................................9
Clearances (Exterior)..............................................10
Venting....................................................................11
OPERATION AND SERVICE .......................................12
Sequence of Operation...........................................12
Electrical Sequence ................................................13
Wiring Diagram .......................................................14
Operating Sequence - Flow Chart ..........................15
Gas Control Valve..................................................16
Measuring Gas Pressures ................................16
Manifold Pressure Adjustment ..........................17
Main Valve Solenoid Connections ....................17
COMMERCIAL GAS WATER HEATER
SERVICE MANUAL
TABLE OF CONTENTS
Gas Control Valve/Burner Area View......................18
Blower Prover Switch - Settings .............................19
Thermostat and Ignition control Board View...........20
White Rodgers Integrated Control - Thermostat.....21
White Rodgers Ignition Control Board ....................21
Pre-Service Checklist .............................................22
TROUBLESHOOTING .................................................23
Ignition Control Board: Error Codes........................23
1 Flash ..............................................................23
2 Flashes ..........................................................23
3 Flashes ..........................................................24
4 Flashes ..........................................................24
6 Flashes ..........................................................24
7 Flashes ..........................................................24
8 Flashes ..........................................................25
Continuous Flash ..............................................25
Continuous On ..................................................25
Integrated Heater Control: Display Lights ..............26
Test 1: 120 VAC to Heater Check ...........................27
Test 2: Polarity Check.............................................28
Test 3: Continuity Check of High Limit (ECO).........29
Test 4: Upper Temperature Probe
Continuity Check.....................................................30
Test 5: Calling for Heat - No Blower Operation.......31
Test 6: Blower On, No Ignition ................................32
Test 7: Blower On, Blower Prover Switch Closed,
No Igniter Operation ...............................................33
Test 8: Igniter Heats, No Main Burner.....................34
Test 9: Igniter Heats, No Main Burner.....................35
Test 10: Main Burner Ignition for Less than
Five Seconds ..........................................................36
Test 11: Water Heater Shutting Off Below Setting ..37

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Servicing should only be performed by a Qualified Service Agent
INTRODUCTION
INTRODUCTION
This Service Manual is designed to be an aid in servicing and troubleshooting A. O. Smith
Master-Fit models BTR 500 Series 120/121 commercial water heaters. The instructions
and illustrations contained in this service manual will provide you with troubleshooting
procedures to verify proper operation and to diagnose and repair common service
problems.
This Service Manual does not replace or supersede the instruction manual that came with
the water heater. Always refer to the instruction manual that came with the water heater for
complete installation instructions. If the instruction manual is not available, copies can be
obtained from the manufacturer’s web site or by calling the toll free phone number shown
on the back cover of this service manual.
QUALIFICATIONS
Servicing the products referenced in this manual requires the ability (in the field involved)
equivalent to that of a Qualified Service Agent as defined by the American National Standards
Institute (ANSI) below. Installation skills such as plumbing, air supply, venting, gas supply,
electrical supply are required in addition to diagnostic and electrical testing skills.
ANSI Z223.1 2006 Sec. 3.3.83: “Qualified Agency” - “Any individual, firm, corporation or
company that either in person or through a representative is engaged in and is responsible
for (a) the installation, testing or replacement of gas piping or (b) the connection,
installation, testing, repair or servicing of appliances and equipment; that is experienced in
such work; that is familiar with all precautions required; and that has complied with all the
requirements of the authority having jurisdiction.”
SERVICE WARNING
If you are not qualified (as defined by ANSI above) and licensed or certified as required by
the authority having jurisdiction to perform a given task, do not attempt to perform any of
the procedures described in this manual. If you do not understand the instructions given in
this manual, do not attempt to perform any procedures outlined in this manual.
SERVICE REMINDER
When performing any troubleshooting step outlined in this service manual, always consider
the wiring and connectors between components. Perform a close visual inspection of all
wiring and connectors to and from a given component before replacement. Ensure wires
were stripped before being crimped in a wire connector, ensure wires are crimped tightly in
their connectors, ensure connection pins in sockets and plugs are not damaged or worn,
ensure plugs and sockets are mating properly and providing good contact.
Failure to perform this critical step or failing to perform this step thoroughly often results in
needless down time, unnecessary parts replacement, and customer dissatisfaction.

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Servicing should only be performed by a Qualified Service Agent
REQUIREMENTS
REQUIREMENTS
INSTRUCTION MANUAL
Have a copy of the instruction manual that came with the water heater on hand for the
model being serviced. Instruction manuals can be obtained at the A. O. Smith web site
(www.hotwater.com) or by calling technical support at 800 527-1953.
Installation information given in this service manual is not a complete installation instruction.
Installation information covered in this service manual has a limited focus as it applies
to servicing the water heater. This Service Manual does not replace or supersede the
instruction manual that came with the water heater. Always refer to the instruction manual
that came with the water heater for complete installation instructions.
TOOLS REQUIRED
Phillips head screwdriver•
standard screwdrivers•
3/8 and 7/16 inch open end wrench•
set of marked drill bits•
electrical multimeter tester capable of measuring continuity, AC voltage, and DC voltage•
gas pressure gauge or manometer (gauge - AOS pt. no. 9005033105)•
water pressure gauge (AOS pt. no. 9004792105)•
thermometer (AOS pt no. 9005423105 - range 0 - 220 degrees F)•
1/2 inch socket with extension for removal of the clean out cover•
1-1/16 inch socket with extension for anode removal•
TOOLS OPTIONAL
Two digital manometers range -20.00 to +20.00” W.C., resolution 0.01” W.C.•
Recommend UEI model EM200, TPI model 620 or equivalent.

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Servicing should only be performed by a Qualified Service Agent
INSTALLATION CONSIDERATIONS
INSTALLATION CONSIDERATIONS
Installation information given in this service manual IS NOT a complete installation
instruction. Installation information covered in this service manual has a limited focus as
it applies to servicing. This service manual does not replace or supersede the Instruction
Manual that came with the water heater. Always refer to the instruction manual that came
with the water heater for complete installation instructions.
If the instruction manual that came with the water heater is not on hand, copies can be
obtained from the manufacturer’s web site or by calling the toll free phone number shown
on the back cover of this service manual.
WATER PIPING
Closed Water Systems
Water supply systems may, because of code requirements or such conditions as high line
pressure, among others, have installed devices such as pressure reducing valves, check
valves, and back flow preventers. Devices such as these cause the water system to be a
closed system.
Thermal Expansion
As water is heated, it expands (thermal expansion). In a closed system, the volume
of water will grow when it is heated. As the volume of water grows, there will be a
corresponding increase in water pressure due to thermal expansion. Thermal expansion
can cause premature tank failure (leakage). This type of failure is not covered under the
limited warranty. Thermal expansion can also cause intermittent temperature-pressure relief
valve operation: water discharged from the valve due to excessive pressure build up. This
condition is not covered under the limited warranty. The temperature-pressure relief valve is
not intended for the constant relief of thermal expansion.
A properly sized thermal expansion tank should be installed on all closed systems to control
the harmful effects of thermal expansion. Contact a local Qualified Service Agency (page 3)
to have a thermal expansion tank installed.
GAS PRESSURE REQUIREMENTS
Table 1 shows supply and manifold gas pressure requirements for BTR 500/A 120 - 121
model water heaters. Supply gas pressure is the pressure of fuel gas being supplied to the
water heater. Manifold gas pressure is the pressure of the gas being supplied to the water
heater’s burners.
Supply gas pressure should be measured twice. One measurement while the water
heater is not firing (static) and again while the water heater is firing (dynamic). If the
supply gas pressure drops more than 1.5” W.C. between the static and dynamic pressure
measurements, this may indicate the gas line and/or gas regulator to the water heater is
undersized. See the gas line requirements in the Instruction Manual that came with the
water heater.

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Servicing should only be performed by a Qualified Service Agent
INSTALLATION CONSIDERATIONS
AIR REQUIREMENTS
Carefully review the requirements for combustion and ventilation air in the instruction
manual that came with the water heater. Failure to meet these requirements when the
water heater is installed or overlooking their importance when servicing the water heater
often results in operational problems (some are listed below), needless down time,
unnecessary parts replacement, and customer dissatisfaction.
Ensure additional air for combustion and ventilation is provided when additional gas fired
appliances are installed to increase hot water supply in an existing location.
Air Supply
Stoichiometric or theoretical complete combustion requires 10 cubic feet of air per 1,000
BTUH of gas supplied. The National Fuel Gas Code also recommends an additional 2.5
cubic feet of “excess” air. For information on minimum make-up air opening sizes for
various building installations, refer to the National Fuel Gas Code NFPA 54, ANSI Z223.1.
Figure 1
Table 1
NATURAL GAS PROPANE (LP) GAS
‡Maximum Supply Gas Pressure 10” W.C. (2.49 kPa) 12” W.C. (2.99 kPa)
†Minimum Supply Gas Pressure 5.2” W.C. (1.29 kPa) 11” W.C. (2.74 kPa)
*Manifold Gas Pressure 3.5” W.C. (0.87 kPa) 10” W.C. (2.49 kPa)
‡ Maximum supply pressure; readings are taken while gas is not flowing (static pressure) AND while gas is flowing (dynamic pressure).
Supply pressure must never exceed this maximum value.
† Minimum supply gas pressure; readings are taken while gas is not flowing (static pressure) AND while gas is flowing (dynamic
pressure). Supply pressure must never fall below the minimum values. Supply gas pressures should be measured with all gas fired
appliances conencted to a common main firing at full capacity. If supply pressure drops more than 1.5” W.C. as gas begins to flow,
the supply gas system (gas line/regulator) may be restricted or undersized. See the instruction manual for more information.
* Manifold gas pressure; reading can only be taken while gas is flowing. Reading taken should be ± 0.3” W.C. of the listed value.
These water heaters are certified for use without modification for altitudes up to 10,000 feet. For elevations above 10,000 feet
(3,048 meters), see High Altitude Installations section of instruction manual.

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Servicing should only be performed by a Qualified Service Agent
INSTALLATION CONSIDERATIONS
Insufficient Make-up Air, Negative Air Pressure, and Downdrafts
A lack of combustion and ventilation air can create a negative ambient air pressure in the
installed space. The vent system on one or more gas fired appliances can experience down
drafts due to the outdoor air pressure being greater than the ambient air pressure in the
installed space. Where multiple gas fired appliances are installed, one or more gas fired
appliances can “pull air” through the vent system(s) of other appliances installed nearby.
Downdraft Caused by Kitchen Vent Hood
Figure 2
One common example is in a restaurant installation where exhaust vent equipment was not
considered in sizing make-up air requirements. This condition may result in air being back
drafted by the restaurant exhaust equipment through the water heater, causing the draft
proving switch to open and/or erratic heater shutdown. See Figure 2.
Down drafts can cause poor mixing of fuel gas and combustion air in the burners.•
Down drafts can cause flue gases to spill into the installed space.•
Down drafts can cause common service problems such as ignition failure. Down drafts•
can sweep pilot gas away from the spark igniter during ignition and prevent ignition of
the pilot.
Down drafts may cause extremely dangerous conditions such as flame rollout where the•
flames from the main burner “roll out” of the combustion chamber.

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Servicing should only be performed by a Qualified Service Agent
INSTALLATION CONSIDERATIONS
Make-up Air: Direct Communication with Outdoors
A fresh supply of make-up air for combustion can be supplied to the water heater through
make-up air ducts, which directly communicate with the outdoors. (Not Direct Vent.)
Two openings are required: one within 12 inches of the top of the enclosure and one
within 12 inches of the bottom of the enclosure. Each opening must have a free area of
not less than 1 square inch per 4,000 BTUH of the total input of all appliances within
the enclosure. The lower opening primarily provides combustion air. The upper opening
provides vent dilution air and acts as a relief opening for flue gases should the vent become
obstructed or a downdraft condition occur.
Figure 3
Additionally, when the water heater is installed in a confined space and communicating with
the outdoor air, one permanent opening, beginning within 12 inches (30 cm) of the top of
the enclosure, must be permitted where the equipment has clearances of at least 1 inch
(2.5 cm) from the sides and back, and 6 inches (16 cm) from the front of the appliance. The
opening must directly communicate with the outdoors and must communicate through a
vertical or horizontal duct to the outdoors or spaces (crawl or attic) that freely communicate
with the outdoors, and must have a minimum free area of a) 1 square inch per 3,000 BTUH
(7cm2per kW) of the total input of all equipment located in the enclosure and b) not less
than the sum of the areas of all vent connectors in the confined space.

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Servicing should only be performed by a Qualified Service Agent
INSTALLATION CONSIDERATIONS
Contaminated Air
Carefully review the warnings concerning contaminated combustion and ventilation air in the
instruction manual that came with the water heater. Combustion air that is contaminated can
greatly diminish the life span of the water heater and water heater components such as burners,
igniters, flue baffles and vent system components. Propellants of aerosol sprays, beauty shop
supplies, water softener chemicals and chemicals used in dry cleaning processes that are
present in the combustion, ventilation or ambient air can cause such damage.
Vapors from volatile compounds such as solvents, cleaners, chlorine based chemicals and
refrigerants in addition to being highly flammable in many cases, can also react to form
highly corrosive substances such as hydrochloric acid inside the water heater’s combustion
chamber. The results can be hazardous and cause product failure.
Contaminated Air Causes Aggressive Corrosion of Water Heater Components
(Burners, Igniters, Flue Baffles, Vent System, Sheet Metal Parts)
Figure 4
CLEARANCES (WATER HEATER)
A 24-inch clearance for all serviceable parts is recommended. See also Figure 5 and
Table 2. You may also refer to the instruction manual or to the label on the water heater
for clearances applicable to your specific model.
Minimum Clearances to Combustible Surfaces
Figure 5

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Servicing should only be performed by a Qualified Service Agent
INSTALLATION CONSIDERATIONS
Table 2
MINIMUM CLEARANCES TO COMBUSTIBLE SURFACES
“A” - Right Side “B” - Left Side “C” - Back
5” (12.7 cm) 5” (12.7 cm) 5” (12.7 cm)
A, B, and C clearances to non-combustible surfaces is “0” inches. A 20” clearance to cover remains unchanged.
CLEARANCES (EXTERIOR)
The illustration below shows the required clearances for venting units using natural draft venting.
The vent must extend at least 3 feet above the highest point where it passes through a
roof of a building and at least 2 feet higher than any portion of a building within a horizontal
distance of 10 feet (for vents of 12 inches in diameter or less).
Reference: NFPA 54 ANSI Z 223.1.
Figure 6

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Servicing should only be performed by a Qualified Service Agent
INSTALLATION CONSIDERATIONS
VENTING
The BTR 500 water heater is classified by ANSI as a Category I (non-condensing, negative
pressure venting) appliance. It is approved for type B vent. The blower (draft inducer) does
not pressurize the exhaust.
NOTE: This section of the service manual is not a complete venting installation instruction.
Refer to the instruction manual that came with the water heater; ensure the venting has
been installed per all instruction manual requirements. Installation must also conform with
the current edition of the National Fuel Gas Code (NFPA 54/ANSI Z223.1). Costs to correct
installation errors are not covered under the limited warranty.
Figure 7
For larger applications, BTR 500 water heaters can be common vented together, either
in a tapered manifold or a constant size manifold. See Figure 8. In such cases, follow
the National Fuel Gas Code requirements for the sizing and installation of fan-assisted
products. The BTR 500 model may be common vented only with other Category I
appliances.
Figure 8
Chimney
A minimum of 1/4”
rise per foot of
horizontal vent is
required.
Tapered Manifold
Constant Size Manifold

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Servicing should only be performed by a Qualified Service Agent
OPERATION AND SERVICE
OPERATION AND SERVICE
SEQUENCE OF OPERATION
1. Call for heat is activated when temperature sensed from Thermistor Probes falls below
the Thermostat setting.
2. Blower (Draft Inducer) is energized.
3. Ignition Control Board verifies that the Blower Prover Switch is closed and that the
Blower (Draft Inducer) is operating.
4. Igniter is energized.
5. Gas Valve is energized and burners ignite
6. Ignition Control Board verifies flame at burners.
7. Water is heated to Thermostat set point.
8. Gas Valve is de-energized.
9. Blower runs for purge period and is de-energized.
10. Ignition Control Board goes into standby mode and Blower Prover Switch Opens.
Blower (Draft Inducer)
Thermistors
(probes)
Hot Surface Igniter
(Not Shown)
Main Gas
Valve
Main
Burner
Figure 9

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Servicing should only be performed by a Qualified Service Agent
OPERATION AND SERVICE
ELECTRICAL SEQUENCE
1. Switch Power on to unit.
2. Thermostat calls for heat.
3. Ignition Control Board performs diagnostic check on system components.
4. On completion of diagnostics check, the Ignition Control Board energizes the Blower
(Draft Inducer).
5. The Blower (Draft Inducer) begins drawing air through appliance, closing the Blower
Prover Switch.
6. On completion of Blower Prover Switch engagement, the Ignition Control Board begins
the ignition cycle.
7. The Ignition Control Board provides power to the Silicon Nitride Igniter.
8. The Silicon Nitride Igniter heats up for approximately 17 to 20 seconds.
9. At the end of Silicon Nitride Igniter’s warm-up, the Ignition Control Board opens the
Gas Valve.
10. From the time the Gas Valve opens, the Ignition Control Board waits 3 seconds
and then shuts off power to the Silicon Nitride Igniter.
11. From the time the Silicon Nitride Igniter’s power is shut off, the Ignition Control
Board waits 3 more seconds to monitor the Flame Sensor.
12. If the Ignition Control Board does not detect flame at the burners, it will de-energize the
Gas Valve and run the Blower for approximately 20 seconds to purge the combustion
chamber. The Ignition Control Board then restarts at Step 7 for up to 2 more trials
for ignition. After the third failed trial for ignition, the Ignition Control Board locks out
for one hour. At the end of this lock out period, the Ignition Control Board will restart
at Step 3 for three more trials. NOTE: The one hour lock out period can be reset by
cycling power to the water heater off and on again.
13. If the Ignition Control Board detects a strong flame from the Flame Sensor, it will remain
in the heating mode until the Thermostat is satisfied.
14. When the Thermostat is satisfied, the Ignition Control Board will de-energize the Gas
Valve and run the Draft Inducer for approximately 20 seconds to purge the combustion
chamber. The Ignition Control Board will then go into standby mode.

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Servicing should only be performed by a Qualified Service Agent
OPERATION AND SERVICE
WIRING DIAGRAM
THERMOSTAT
IGNITION BOARD
UPPER
PROBE/
PROBE
THERMOPLASTIC OR EQUIVALENT.
MUST BE REPLACED USE ONLY TYPE 105 C
IF ANY OF THE ORIGINAL WIRE AS SUPPLIED
BOARD, DIGITAL THERMOSTAT AND CONTROLS.
WHEN EQUIPPED WITH WHITE-RODGERS IGNITION
WIRING DIAGRAM FOR BTR 500
BY INSTALLER
FACTORY INSTALLED
120 VAC CIRCUIT
1a 1 1b
W - WHITE
BL - BLUE
G - GREEN
Y - YELLOW
R - RED
BR - BROWN
BK - BLACK
GROUND
TO EARTH
EARTH GROUND
NEUTRAL
HOT 120 VAC
BK
W
Y
Y
W
RR
R
R
BL
BR
G
R
R
BK
Y
W
R
R
BK BK
SENSOR
IGNITER/FLAME
LOWER
ECO
BLOWER PROVER
PRESSURE SWITCH
INDUCER
OFF
IN
PSI
IN
PSI
OFF
ON ON
NOTE:
Must be properly grounded
and have correct polarity
connections.
Figure 10
!WARNING
Disconnect from electrical supply before servicing unit. Replace all doors and panels
before operating the water heater.

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Servicing should only be performed by a Qualified Service Agent
OPERATION AND SERVICE
OPERATING SEQUENCE - FLOW CHART
Figure 11
Power On
Call for Heat
Self diagnostic check is performed
(Correct state of Blower Prover Switch and ECO is verified)
(polarity , earth ground , and Igniter presence are verified )
YES
Blower Prover Switch (N.O.) Contacts
Close at – 2.85“ W.C. ± 0.13” W.C.
Ignition Control Board
Sends Voltage (80-120 VAC)
to Igniter for 17-20 Seconds.
YES
Ignition Control Board Energizes
Gas Valve (24 VAC)
Igniter De-energized After 3 Seconds
Ignition Control Board Waits 3
More Seconds For “Strong” Flame
Sense Signal (2.0 uA DC or more)
Tank Heated to Set -Point
Ignition Control Board
De-energizes Gas Valve
YES
Blower Runs 60 Seconds
Post Purge Cycle and
Shuts Off
Blower Prover Switch Contacts Re-open
Ignition Control Board Goes into Standby Mode
Control Locks Out - LED
Displays 2, 6, or 8
Flash Error Code
(See Error Code Chart )
NO
Control Locks Out
Displays 3 Flash
Error Code
NO
Below 0.1 uA DC Flame Sense:
Heater Will Try to Ignite 3 Times
Control De-energizes Gas Valve
Blower Runs for Post Purge Period
Control Locks Out for 1 Hour
Displays 1 Flash Error Code
Between 2.0 and 0.1 uA DC Flame Sense
Heater Will Continue to Operate
Displays 7 Flash Error Code
(Weak Flame Sense)
NO
Blower (Draft Inducer)
Motor is Energized

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Servicing should only be performed by a Qualified Service Agent
OPERATION AND SERVICE
GAS CONTROL VALVE
This gas valve is a 24 volt AC combination-step opening valve. It includes two valves
assembled in parallel, connected by a wiring harness. Note that the valves have fixed
pressure regulation and are not adjustable. However, the manifold (outlet) pressure is
adjustable as described on the next page.
IMPORTANT:
For complete device shut-off, both gas control knobs must be in the OFF position.•
Both gas control knobs must be in the same position for operation or shutoff.•
Do not alter or remove the wiring harness.•
Do not apply a jumper across the valve lead wires or short them together.•
Inlet
Outlet
Inlet Pressure Taps
Gas Control Knobs
Manifold Pressure
Taps
Wiring Harness
TOP VIEW OF GAS VALVE
Main Gas
Regulators
(Outlet Pressure
Adjustment)
Figure 12
Measuring Gas Pressures
The supply gas pressure is measured at the inlet pressure tap when the gas is flowing. The
manifold gas pressure is measured at the manifold pressure tap when the gas is flowing.

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Servicing should only be performed by a Qualified Service Agent
OPERATION AND SERVICE
Manifold Pressure Adjustment
The main gas regulators are found beneath the silver or black cap screws. (Natural Gas
valves have silver caps; Propane valves have a black caps). Remove the caps to access
the outlet (manifold) pressure adjustment screw. IMPORTANT: Ensure that the outlet
pressure matches the manifold pressure that is listed on the water heater rating plate.
Natural Gas valves are factory preset to 3.5 inches W.C. The full rate outlet pressure•
range is between 3 and 5 inches W.C.
Propane (LP) valves are factory preset to• 10.0 inches W.C. The full rate outlet pressure
range is between 8 and 12 inches W.C.
Caution: Always test the manifold pressure at the outlet when the gas is flowing.•
Wiring Harness
TOP VIEW OF GAS VALVE
Main Gas
Regulators
(Outlet Pressure
Adjustment)
Lead Wires
(24-Volt Main Valve
Solenoid Connections)
Figure 13
Main Valve Solenoid Connections
The figure above shows the two 24-volt main valve (MV) solenoid connections. The two
yellow wires from the 12-pin ignition board plug connect to these leads.

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Servicing should only be performed by a Qualified Service Agent
OPERATION AND SERVICE
GAS CONTROL VALVE/BURNER AREA VIEW
Honeywell Gas
Valve
Main Burner
Shield
Rollout Shield
Radiation
Shield
Main Burner with
Hot Surface Igniter
(HSI) mounted
Figure 14
Table 3
HOT SURFACE IGNITER (HSI)
Volts AC Nominal 80 VAC
Ohms Resistance 11.0 - 20.0 @
77° F (25° C)
NOTICE FLAME ROD CROSSES PATH OF
FLAME 0.1” to 0.25”.

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Servicing should only be performed by a Qualified Service Agent
OPERATION AND SERVICE
BLOWER PROVER SWITCH - SETTINGS
Vent Connection
Exhaust/Outlet
Blower Prover Switch
Blower (Draft Inducer)
Optional Hot Water Outlet
Figure 15
Table 4
BLOWER PROVER SWITCH TABLE
BTR Model Pressure Setting to Close Switch (Inches W.C.)
500/A -2.85” ± 0.13”
NOTE: The Blower Prover Switch contacts are normally open and will close on a fall in
pressure. This will be a negative pressure (i.e., a vacuum).

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Servicing should only be performed by a Qualified Service Agent
OPERATION AND SERVICE
THERMOSTAT AND IGNITION CONTROL BOARD VIEW
Figure 16