Bradford White EF120T4003N3 User manual

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Manual 238-53597-00B REV 5/20
SERVICE
MANUAL
Troubleshooting Guide
and Instructions for Service
(To be performed ONLY by
qualified service providers)
Models Covered
by This Manual:
EF120T4003N(A)3
EF120T5003N(A)3
Commercial Ultra High Efficiency Models
with Direct Spark Ignition
Effective: April, 2020
ECO 8160

2
Ultra High Efficiency Models with Direct Spark Ignition
Table of Contents
Introduction………………………………………………………………………………….....
..3
How to Use This Manual……………………………………………………………………..
..4
Tools Required for Service…………………………………………………………………..
..4
Features………………………………………………………………………………………..
..5
Specifications………………………………………………………………………………….
..6
Sequence of Operations………………………………………………………………………
..9
Building Management System (BMS)……………………………………………………….
.10
Troubleshooting……………………………………………………………………………….
.11
Service Procedure I: Thermostat Circuit Testing and Replacement…………………….
.19
Service Procedure II: Combustion System Testing and Replacement……………….....
.23
Service Procedure III: Burner Tube Inspection and Replacement……………………….
.27
Service Procedure IV: Gas Valve Replacement……………………………………………
.29
Service Procedure V: Blower Testing and Replacement…………………………………
.30
Service Procedure VI: Blocked Vent Pressure Switch Testing and Replacement……..
.32
Service Procedure VII: Flame Sensor Testing and Replacement……………………….
.35
Service Procedure VIII: Spark Rod Gap Adjustment and Replacement…………………
.37
Service Procedure IX: Ignition Control Board Replacement………………………………
.39
Service Procedure X: Transformer Replacement………………………………………….
.40
Service Procedure XI: Vent Safety Switch Testing and Replacement…………………..
.41
Service Procedure XII: Power Anode Inspection and Replacement…………………….
.43
Water Heater Installation Checklist………………………………………………………….
.44
Water Heater Service Report…………………………………………………………………
.45
Glossary of Terms……………………………………………………………………………..
.46
Notes……………………………………………………………………………………………
.46
2

3
Introduction
The 120T Ultra High Efficiency Water Heater is designed to deliver a high thermal efficiency rating, in
a quiet running unit with venting options that allow for installation flexibility. Several technologically
advanced design features are incorporated in the design that will require additional knowledge on the
part of the qualified service provider. The information in this manual will instruct service and
maintenance professionals on the function, proper diagnosis, and repair of this water heater.
The 120T Ultra High Efficiency Water Heater uses a low NOx premix power burner located at the top
of the water heater to direct a turbulent flame down into a submerged combustion chamber. The
turbulence causes a thorough mixing of gas and air for optimum combustion. The combustion gases
then travel through a three pass flue system, keeping the gases moving at a high velocity. The
combination of high turbulence and velocity results in an optimum transfer of heat from the flue gases
into the water.
Burner operation is controlled using an electronic ignition control board. The control board monitors the
status of the electronic thermostat, vent temperature limit switch, vent system pressure switch, a flame
sensor, spark rod, and gas valve. The control board contains programming which determines the
sequence of operation and timings for purge periods, trial for ignition, flame sensing, and lockouts. The
control board modulates the water heater to adjust the firing rate to account for varying hot water
demands. Additionally, the control board will provide diagnostic information both on the control board
and digital display to help in determining the cause of system lockouts.
The contents in this manual are detailed informational tools to assist in the proper diagnosis of the 120T
Ultra High Efficiency Water Heater operational faults. Please read the entire Service Manual, which
provides detailed information regarding the 120T Ultra High Efficiency Water Heater operation and
installation specific concerns.
How To Use This Manual
It is intended for this manual to be used by qualified service personnel for troubleshooting analysis and
repair of the 120T400/500 models. Understanding the sequence of operation section of this manual will
contribute greatly to troubleshooting this product.
An Installation Checklist is shown on page 44. Compare the installation against this installation checklist
to confirm all requirements are met.
A Service Report is shown on page 45. Completing this form will assist in the troubleshooting efforts.
Should you need to call for technical support, please provide the information shown on this form to the
support technician to ensure accurate troubleshooting.
Troubleshooting begins with System Observation to determine failure mode as indicated by error codes
on the system display. Troubleshooting continues with Failure Modes and Probable Cause, directing
the service provider to a series of test procedures to determine the root cause of failure. Component
replacement procedures directly follow the test procedures for a given component.
In some difficult to diagnose conditions, it may be necessary to isolate the heater from the vent system
to determine root cause.
Contact Technical Support immediately if diagnosis is not determined using the methods described in
this service manual.
3

4
Tools Required for Service
Manometer: Two types available, a liquid “U” tube type or a digital (magnehelic) type. This device is
used to measure gas and/or air pressures and vacuum.
Multi-Meter: A digital type is strongly recommended. This device is used to measure electrical values.
The meter must have the capability to measure volts AC, volts DC, amps, micro-amps, and ohms.
Thermometer: Used to measure water temperature. An accurate thermometer is recommended.
Water Pressure Gauge: Used to measure water supply pressure, and to determine tank pressure by
adapting to the drain valve of the heater.
Jumper Leads: A length of wire (12 in. minimum) with an alligator clip at both ends.
Various Hand Tools: Pipe wrench, channel locks, open end wrench set, 12 in. crescent wrench, Allen
wrench set, Torx bit set, screwdrivers (common & Phillips), long reach (12 in.) magnetic tip Phillips
head screw driver #2 tip, 1/4 in. nut driver, pliers (common & needle nose), socket set including a 1-
1/16 deep well socket, wire cutters, wire strippers, wire crimpers, torpedo level, small shop vac, step
ladder, and flashlight.
Features
Features of the Honeywell Integrated Control System
xWater heater digital display on control board for setting and displaying the temperature setpoint.
Pressing temperature UP and DOWN buttons changes the temperature setpoint. Temperature
format may be displayed in °F or °C.
xSingle control board with plug-in wiring controls temperature, ignition, and blower operation.
xPlug-in wiring reduces chance of miswiring.
xBurner ignition with direct spark ignition - A high voltage spark jumps from the spark rod to the
burner surface to ignite the gas.
xWater heater digital display will show diagnostic codes in the event the water heater needs servicing.
Aids in diagnosing and servicing the water heater.
xWater heater digital display can show previous error code history to further aid in servicing the water
heater.
4

5
Specifications
DIMENSIONS (INCHES)
Model No.
Input
Rate
BTU/h
Storage
Capacity
U.S.
Gallons
A
Height
B
Floor to Alt.
Hot Water
Outlet
C
Dia.
D
Floor to
Vent
Outlet
E
Floor to
Inlet
Water Conn.
F
Floor to
T&P
Valve Conn.
G
Floor to
Hot Outlet
Water Conn.
H
Floor to Top
of Heater
120T400
399,999
119
77 1/8
70 3/8
33
6 ¾
12 ¼
58 ½
61 ¼
68 ¼
120T500
499,999
119
77 1/8
70 3/8
33
6 ¾
12 ¼
58 ½
61 ¼
68 ¼
Model No.
Input
Rate
BTU/h
Storage
Capacity
U.S.
Gallons
J
Floor to
Air
Intake
K
Floor to
Gas
Conn.
Front
Water
Conn.
Dia.
Space
Heating
Conn.
Dia.
Gas
Conn.
Dia.
Relief
Valve
Open
Shipping
Wt.
(LBS)
120T400
399,999
119
71
73 ¾
1 ½
1
1
1
1120
120T500
499,999
119
71
74 7/8
1 ½
1
1
1
1135
DIMENSIONS (MILLIMETERS)
Model No.
Input
Rate
KW
Storage
Capacity
Liter
A
Height
B
Floor to Alt.
Hot Water
Outlet
C
Dia.
D
Floor to
Vent
Outlet
E
Floor to
Inlet
Water Conn.
F
Floor to
T&P
Valve Conn.
G
Floor to
Hot Outlet
Water Conn.
H
Floor to Top
of Heater
120T400
117.22
450
1959
1787
838
171
311
1486
1556
1733
120T500
146.54
450
1959
1787
838
171
311
1486
1556
1733
Model No.
Input
Rate
KW
Storage
Capacity
Liter
J
Floor to
Air
Intake
K
Floor to
Gas
Conn.
Front
Water
Conn.
Dia.
Space
Heating
Conn.
Dia.
Gas
Conn.
Dia.
Relief
Valve
Open
Shipping
Wt.
(LBS)
120T400
117.22
450
1803
1873
38
25
25
25
508
120T500
146.54
450
1803
1902
38
25
25
25
515
5

6
Specifications
Power Supply Dedicated 120 VAC, 60 Hz, (15A GFI recommended)
Gas Supply Minimum 1 in. NPT
(schedule 40 black iron pipe recommended)
Approved Gas Type Natural
Gas Pressure (Nat.) 14”W.C. maximum static, 4.5”W.C. minimum running
(recommend 7”W.C. min running)
Venting System Power vent, balanced direct vent or unbalanced direct
vent. See vent tables on page 7.
Approved Venting Materials PVC and CPVC venting
Minimum Clearance for
Servicing
18 in. from top, 24 in. from front, 4 in. sides and rear.
Maximum Water Supply
Pressure 150 PSI
Thermostat Sensor
11,900 Ohms @ 70°F, ECO opens @ 207°F maximum.
Redundant sensor for ECO. Sensor inside well for easy
replacement of sensor.
Control Display
Digital display, 24 volts. Temperature range: 100 to
183°F. Used to set tank temperature (°F or °C), show
operating status, display error codes, error code history,
and limit maximum setpoint temperature.
Control Board
Operates on 24 volt from transformer. Controls tank
temperature, ignition functions, combustion blower. See
ignition timings in sequence of operation for Integrated
Control.
Transformer 120 VAC primary, 24 VAC secondary, 40 VA.
Spark Rod Igniter 0.22 in. nominal gap to the burner surface.
Flame Sensor Output Minimum 1 micro amp. Typical range 5 to 30 micro
amps.
Gas Valve Negative regulation, 24 VAC, 1/2 in. PSI max., 4.5”
W.C. minimum running inlet.
Vent Safety Switch Normally closed, opens @ 190°F, manual reset.
Blocked Exhaust Vent
Pressure
24 VAC, normally closed, opens when pressure
increases to +2.70”W.C.
Blower 120 VAC, 60 Hz, 2.5-5.5 amps, full blower RPM
Combustion Levels CO2: 8-9.5%, CO: less than 0.04% (400 PPM) air free
6

7
Specifications
Vent Tables
Power Direct Vent and Power Vent Maximum Vent Length
(Combined Maximum Length for Intake and Exhaust)
Air intake CANNOT exceed exhaust by more than 30 ft
WARNING
Ensure that the elbows are counted when determining total vent length. See below and the Installation and Operation
Manual for more information.
WARNING
The 120T400/500 model is NOT approved for 2 in diameter vent pipe. Venting with 2 in pipe may result in damage to
the water heater or cause an unsafe condition. DO NOT use 2 in vent or air intake pipe.
Notes:
1) Multiply the total number of 90° elbows (intake and exhaust) by 5 ft. DO NOT include the 4 in termination fittings or 4 in
condensate elbow.
2) Multiply the total number of 45° elbows (intake and exhaust) by 2 1/2 ft.
3) Add this to the total length of straight pipe - intake and exhaust.
4) The total of all elbows and straight pipe: intake and exhaust must not exceed maximum lengths from tables above.
Example:
A 4 in balanced direct vent system has 10 ft of straight exhaust pipe and 10 ft of straight intake pipe. It has 1- 90° elbow in
the exhaust and 1- 90° elbow in the intake. It has 1- 45° elbow in the exhaust and 1- 45° elbow in the intake.
Therefore:
2- 90° elbows x 5 ft = 10 ft.
2- 45° elbows x 21/2 ft = 5 ft.
20 ft of straight pipe + 10 ft + 5 ft = 35 ft.
System is within “Maximum Combined Length” from table above.
120T-400-3N(A) 399,999 BTU/hr
120T-500-3N(A) 499,000 BTU/hr
3 in. Vent Pipe
Power Direct Vent
Power Vent
Power Direct Vent
Power Vent
Max. Intake Length 65 ft. N/A 65 ft. N/A
Max. Exhaust Length 65 ft. 65 ft. 65 ft. 65 ft.
4 in. Vent Pipe
Power Direct Vent
Power Vent
Power Direct Vent
Power Vent
Max. Intake Length 100 ft. N/A 100 ft. N/A
Max. Exhaust Length 100 ft. 100 ft. 100 ft. 100 ft.
6 in. Vent Pipe
Power Direct Vent
Power Vent
Power Direct Vent
Power Vent
Max. Intake Length 120 ft. N/A 120 ft. N/A
Max. Exhaust Length 120 ft. 120 ft. 120 ft. 120 ft.
7

8
Sequence of Operations
1. Thermostat calls for heat.
2. Combustion blower starts at a 3,000 RPM “soft” start light off.
3. Blower pre-purge period of approximately 15 seconds.
4. Ignition control board runs an internal verification safety check for approximately 15 seconds.
5. Trial for ignition (approximately 5 seconds per trial, 3 trials total):
a. Flame establishing period (3 seconds), gas valve opens, sparks from spark rod to burner surface to
ignite the gas.
b. Burner on, flame proving period (2 seconds). Requires a minimum of 1 microamp through the flame
sense rod to prove flame.
c. If the blocked vent pressure switch contacts (normally closed) are open, then the ignition sequence
will not start and error code “67” (pressure switch failed to close/open or vent safety switch failed to
close/open) will flash once on the digital display. The unit will then go into pre-purge/“Hold” while the
unit is waiting for the issue to be corrected. If the issue continues to occur, the digital display with flash
error code “137” (pressure switch is open, or vent safety switch is open) while the unit is waiting to
restart (5 minutes) the normal sequence of operation.
6. Once the flame signal is verified, the blower will remain at the “soft” start RPM for 5 seconds to stabilize
the flame.
7. Steady state operation – Burner continues to operate until:
a. The thermostat circuit opens, gas valve closes, and blower continues to operate for 30 second post-
purge period.
b. If the blocked vent pressure switch contacts open (normally closed) while the burner is on, then the
gas valve closes, and the unit will retry a normal sequence of operation. If issue remains on restart,
the unit will go into recycle as described in 5c.
8. The RPM of the blower will modulate depending on the heater demand. The control allows for a turn down
ratio (TDR) of approximately 3:1. Generally, the blower will operate at higher speeds if the thermostat
remains far from the setpoint and at lower speeds as the thermostat approaches the setpoint.
9. Thermostat is satisfied.
10. Gas valve closes and burner is extinguished.
11. Blower post purge for 30 seconds at maximum RPM.
8

9
Sequence of Operations
Lockout Conditions
The system will go into lock out mode for the following reasons:
1. ERROR CODE 110
a. Control board will go into soft lockout if the main burner cannot be lit or fails to prove flame after 3 ignition
trials. The water heater digital display indicates a lockout condition by showing error code 110 with “Service
Needed” on the control board’s digital display. Refer to error codes in the diagnostic section of this Service
Manual. In a soft lockout condition, the control will wait for 15 minutes and then make 3 more attempts to
light the main burners. Soft lockout reset is accomplished by depressing the lower right button under “Reset”
for 3 seconds.
2. ERROR CODE 80
a. If the temperature at the top of the tank should exceed 207°F, then the high limit control will shut off the
burner and the water heater will go into a hard lockout. Error code 80 will be shown on the control board’s
digital display. The control board can only be reset in the Service Mode, which is detailed in the
Troubleshooting section of this Service Manual (pg 11).
3. ERROR CODE 67
a. If the exhaust terminal becomes blocked or the condensate elbow fails to drain condensate, the normally
closed exhaust pressure switch will open, the gas valve will close, and error code 67 will appear on the
digital display. When the condition is corrected, the error code will disappear, and the water heater will
resume normal operation. No resetting of the control board is needed for the pressure switch error code.
b. If the vent safety switch located near the exhaust pressure switch should open, the gas valve will close, the
blower will post-purge, and error code 67 will appear on the control board’s digital display. The lockout
condition will reset once the problem is corrected and the switch is reset. Refer to Vent Safety Switch
Testing and Replacement in this Service Manual (pg 42).
c. The pressure switch and temperature switch are wired in series. As a result, the water heater will not
function unless both switches are operational.
Connection/Wiring Diagram
9

10
Building Management System (BMS)
The 120T can be equipped with a gateway kit that will facilitate a Building Management System
(BMS) connection to Modbus or Bacnet®. This kit is sold separately and is not factory installed. A full
installation, operation, and troubleshooting manual is provided with the gateway kit.
CAUTION
Before beginning any Troubleshooting operations listed below, please note that the gateway kit and
BMS may need to be disconnected from the heater. Please ensure this has been completed before
proceeding with any troubleshooting operation that may be impacted by settings in the BMS.
10

11
120T Control Board Schematic
Troubleshooting
System Observation for 120T400/500 Models with Direct Spark Ignition
Water Heater Fault: Water heater does NOT operate.
Display Error Code: Water heater digital display does
NOT operate - blank display.
Is 24-28 VAC present
between red and black wire
pin connections on the back
of control board?
Verify secondary voltage at the control
board.
Refer to control board illustration.
Voltage at connector location J8 across
blue and yellow wires should be 24-28
VAC. If not, check transformer. Replace
transformer if defective.
Does the water heater digital
display operate? Increase
thermostat setting if tank is warm.
Digital display
operates–see
next page.
Check main power supply to water heater.
Check fuse, circuit breaker, plug receptacle, line
cord, and wiring to water heater.
Check to make sure switch on front of control
board is in the ON position.
Replace digital display.
Replace control board.
Check wire
harness for proper
continuity.
Check wires for proper
termination to control board. Are
wire terminations connected
properly to digital display?
N
Y
N
Y
Y
Refer to control board illustration.
Voltage at transformer across black and
white wires should be 110-120 VAC.
Verify 120V from the power switch.
Verify primary voltage at the transformer.
WARNING
120 volt potential exposure. Use caution making
voltage checks to avoid personal injury.
CAUTION
Use caution to NOT damage connectors when
making voltage measurements or jumping terminals.
Black & White
wires
Yellow & Blue
wires
11

12
120T Control Board Schematic
WARNING
120 volt potential exposure. Use caution making
voltage checks to avoid personal injury.
Troubleshooting
CAUTION
Use caution to NOT damage connectors when
making voltage measurements or jumping terminals.
Error code 62 on display. Measure voltage
between black and white wires, of the 3
wire harness,at the blower (make sure the
digital display shows “heating” in the status
mode, if not increase the setpoint). Is there
110-120 VAC?
Verify 120V from power switch. Replace
power cord/blower harness if digital
display shows “heating” and no voltage
is present to the blower.
Check that the 5 wire blower
modulation harness is plugged
in to the blower.
Plug in the wire harness (If this
harness is unplugged blower will
run constantly).
See Combustion System Testing
and Replacement (pg 23).
Does burner continue until
thermostat set point is
reached? See setting
display in Service Mode
and displaying
temperature sensors.
Does blower post-purge for
30 seconds?
System O.K.
Check to see if digital
display shows any other
error codes (67–pressure
switch, 67–vent safety
switch, or 80–high limit).
If so, refer to the
appropriate section(s) for
testing and replacement.
Remove high voltage wire connected at
the spark rod and hold approximately 1/4”
from metal ground with insulated pliers
during the ignition cycle (3 second spark
trial period). Is there spark to ground?
Check resistance of high voltage
cable. Resistance should be 0-1
ohms. If resistance is high, replace
spark cable. If spark cable is good,
replace control board.
Check continuity of spark rod and spark
rod gap to burner (see Spark Rod Gap
Adjustment, pg 37).
Error code 110 on display.
See main burner lights, no
flame signal in section
Combustion System Testing
and Replacement (pg 23).
Continued from
previous page.
Does combustion
blower operate?
Can sparking be
seen/heard at the spark
rod to the burner?
Replace blower.
Replace control board.
Measure voltage
between yellow (J-2)
and ground. Is there
17-30 VDC?
N
N
N
N
N
N
N
N
Does main burner light?
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
12

13
Troubleshooting
Water Heater Display and Control Buttons
Step 1: Press and hold the lower right button under “Next” in the lower right display for at least 3 seconds.
Step 2: The digital display will show the flame sense current in microamps when the burner is operating.
Step 3: Press the lower right “Next” button and the digital display will flash and show the number of any alert codes. If
alerts are present and the unit is not operating, refer to proper service procedures in this manual.
WARNING
The following procedure is for service and installation personnel only. Resetting lockout conditions without correcting
the malfunction can result in a hazardous condition.
13

14
Troubleshooting
Step 4: Press lower right “Next” button and the digital display will flash and show the number of any Lockout codes.
Step 5: Press lower right “Next” button and the digital display will show the temperature sensor reading.
Step 6: Press lower right “Next” button and the digital display will show the manual firing rate adjustment. This function is
not currently used. Any adjustment made has no effect.
Step 7: End of screens in Service Mode. Press “Done” button on lower left to exit Service Mode back to DHW setpoint in
the User Mode.
NOTICE
The screens will stay in the Service Mode for 12.5 minutes after the last button press for viewing unless
“Done” button is pressed to exit Service Mode.
14

15
Troubleshooting
To Increase Setpoint Temperature
Step 1: Press and hold “Temperature Up” button until desired setpoint temperature appears on the display.
Step 2: Press “DONE” button for new setting to take effect immediately. If the “DONE” button is not pressed, the new
temperature setting will take effect in approximately 10 seconds.
To Decrease Temperature Setpoint
Step 1: Press and hold “Temperature Down” button until desired setpoint temperature appears on the display.
15

16
Troubleshooting
Step 2: Press “DONE” button for new setting to take effect immediately. If the “DONE” button is not pressed, the new
temperature setting will take effect in approximately 10 seconds.
To Change Temperature Format in Display from q
q
F to q
q
C or C to F
Enter “Set-Up Mode” by pressing both UP/DOWN buttons together for 3 seconds.
NOTICE
Pressing the “NEXT” button instead of “DONE” will enter the display to show unused screens such as “Stack ----F,
Outdoor ----F, % Rate (Shows percentage of full input rate for Lightoff rate), Outlet ----F, Inlet ----F, Delta T ----F.
These screens are not used in our application. Press DONE to exit this screen back to the DHW setpoint display.
16

17
Troubleshooting
SERVICE ERROR CODES AND TROUBLESHOOTING PROCEDURES FOR 120T400/500 MODELS WITH
HONEYWELL LOW FIRE START CONTROL SYSTEM
Error Code
Definition
of Code
Cause of Problem and Actions Taken to Correct
No code –
blank display
xCheck power supply to the water heater.
xMake sure the water heater is plugged in and the breaker is on.
xCheck if there is 120 volts power supply to the line connections on the control board.
xIf 120 volts is present, check for 24 volts output to secondary terminals on the control
board.
xCheck for loose wires, defective transformer.
xCheck wire harness connections from digital display to the control board.
3-48, 58-60 Internal
faults
xVerify wiring to the control board with wiring diagram.
xCheck power supply to make sure voltage and frequency is correct.
xCheck for 24 volts from the transformer to the control board.
xReset the control board by interrupting power or pressing the reset button on the control
board.
49
Voltage
too low or
high
xCheck the control board and digital display connections.
xCheck the control board power supply and make sure that frequency, voltage and VA
meet the specifications. See Service Procedure X: Transformer Replacement (pg 40).
53 Reverse
polarity
xCheck the control board and digital display connections.
xCheck the control board power supply and make sure that frequency, voltage, and VA
capacity of the transformer meet specifications.
xCheck to make sure the wiring connections on the control board from terminals J4-10
and J8-2 are connected.
62 Fan speed
not proved
xCheck the blower modulation wire harness connection from the blower to the control
board at J2 connection.
xMake sure the pin terminals make solid contact.
xMeasure the resistance of each wire in the wire harness from the terminal ends.
xReplace wire harness if defective.
xCheck if there are 17-30 volts DC between the yellow and green wires on the blower 5
wire harness.
67
ILK off
(interlock
off)
xCheck wiring to the normally closed blocked vent pressure switch and vent limit switch
(service panel near vent outlet connection).
xUse a voltmeter to find out if the pressure switch or high limit switch has opened.
xIf so, determine the cause (blocked vent terminal, clogged condensate drain, high
temperature in compartment).
xIf limit switches are closed, check wiring for shorts.
xMeasure continuity.
xIf limit switches and wiring check O.K., replace control board.
17

18
Troubleshooting
80
High limit
(overheat
condition)
x Check the wiring from the sensor to the control board.
x Measure the resistance of each outside wire to the center wire (resistance chart found on
pg 21).
x If either outside wire has a much different resistance reading, replace the sensor.
x Make sure the sensor is securely held inside the well with the clip.
x If the problem persists and the sensor and wiring check O.K., then replace the control
board.
93 DHW/T
emp
sensor fault
x Check the sensor wire harness from the sensor to the control board.
x Make sure there are no loose connections to the control board.
x Check the resistance reading from each of the outside wires to the center (common) wire
(resistance chart on pg 21).
x If the ohm readings are not within 5°F, replace the sensor.
x Replace the control board if the problem persists and the sensor and wire connections are
not defective.
105
Flame
detected
out of
sequence
x Check to see if flame is present inside the combustion chamber before or after the ignition
cycle.
x If so, check to make sure the gas valve is wired correctly.
x Check for voltage at the gas valve connection.
x Replace the gas valve if defective.
x If no flame is visible outside of the ignition sequence/run cycle, then make sure the flame
sensor is wired to the correct terminal.
x Make sure the ignition cable is not crossing the flame sensor wire or ignition ground wires,
and that there is no moisture on the flame sensor.
x If problem persists and all other checks have been verified, replace the control board.
110
Ignition
failure
occurred
x Burner failed to light or stay lit after 3 retries.
x Hold condition – will reattempt ignition after 15 minute waiting period.
x Check gas valve wiring and gas valve operation during the ignition cycle.
x If burner lights but quickly goes out, check the flame sensor wire or the flame sensor.
x If the flame sensor rod is badly corroded with deposits, clean with sandpaper or replace.
x Check the inlet gas supply to make sure the pressure is sufficient and does not drop after
the gas valve opens.
x Make sure the combustion blower is operating during the ignition and run cycle.
x Check the venting system to make sure the inlet and exhaust terminals and venting
system is not blocked.
122
Light-off
rate proving
failed
x If blower speed is not verified from the PWM (Pulse Width Modulation) signal within 5
minutes, the previously described error code 62 changes from a hold condition to this
lockout code condition.
x Check the harness and pin terminals for a good connection to the control board.
x Replace the blower or control board if the wire harness is good.
123
Purge rate
proving
failed
x Check wiring and correct any potential wiring errors.
x Check VFD’s (variable-speed fan drive) ability to change speeds.
x Change the VFD.
x If the fault persists, replace the module.
137
ILK open
(interlock
open)
x Check if blocked vent pressure switches or vent limit switch are open.
x If all switches check O.K., replace control board.
18

19
Service Procedure I:
Thermostat Circuit Testing and Replacement
IMPORTANT NOTE: This procedure assumes a cool tank.
Check sensor. Sensor is held in place with a clip fastened
to the well (see image). Check sensor wire for potential
damage or breaks in the wire insulation. Is the sensor fully
inserted into the well?
Condition: Water heater not operating. Digital display
shows error code 93 (sensor reading faulty).
Unplug or disconnect electrical power to the water heater.
Check continuity of wire harness to sensor. Resistance of
harness should be close to 0 ohms. Replace wire harness
if high resistance is measured (over .5 ohms). Check
wires for intermittent connections, shorts, and/or frayed
insulation. Replace if necessary.
If wire harness is O.K., check sensor resistance detailed in
Appendix A: Sensor Resistance at Various Temperatures,
pg 21. Replace sensor if needed.
Turn power ON to water heater. Run water heater through
heating cycle and verify proper operation. Sensor
temperature can be viewed when burner shuts off (see
section on viewing the digital display in Service Mode).
Condition: Water heater not operating. Digital
display shows error code 80 high water
temperature (over 207°F).
Continued on
next page.
WARNING
DO NOT reset the digital display from the hard
lockout state without correcting the cause of
the overheating condition.
Turn power OFF. Draw water to cool tank below 120°F.
If sensor clip is damaged replace
clip. Replace sensor if damaged.
Check sensor resistance (see Appendix
A: Sensor Resistance, pg 21).
Checking continuity
of sensor across
the two black wires
(disconnected from
control board)
The sensor is located next to the top outlet location
Sensor clip shown
properly installed
WARNING
120 volt potential exposure. Use caution
making voltage checks to avoid personal injury.
CAUTION
Use caution to NOT damage connectors when
making voltage measurements or jumping
terminals.
19

20
Service Procedure I:
Thermostat Circuit Testing and Replacement
WARNING
DO NOT operate the water heater without
verifying that the overheating condition has
been corrected.
Once cause of overheating condition
has been diagnosed and corrected, the
control board may be reset.
x Reconnect and switch on power to the water heater.
x Press button under “Reset” and hold for 3 seconds.
x Set thermostat to the desired setting.
x Water heater will start.
x Monitor temperatures for one complete heating cycle making
sure the maximum tank temperature remains below 207°F.
Condition: Water heater not operating. Digital
display shows error code 80 high water
temperature (over 200°F) (continued from
previous page).
Continued from previous page.
20