Service Manual

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Sequence of Operation
1. Thermostat calls for heat.
2. Combustion blower starts.
3. Blower pre-purge period of 30 seconds.
4. Trial for Ignition (5 seconds, 3 trials).
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 0.8 microamp through flame
sense rod to prove flame.
c. If either blocked vent safety switch contacts (normally closed) or blocked vent pressure switch
contacts (normally closed) are open, then the ignition sequence will not start and an error code 29
(Pressure switch failed to close or open) will be shown on the display.
5. Steady State Operation: Burner continues to operate until:
a. Thermostat circuit opens, gas valve closes, blower continues to operate for 30 second post-purge
period.
b. If the normally closed blocked vent pressure switch opens, the gas valve closes, the blower
continues to operate indefinitely and error code 29 will be displayed after a couple minutes with
“Service Needed”, “Pressure Switch”.
c. If the normally closed 1
st
Pass Collector vent safety switch opens, the gas valve closes, the blower
post- purges, then shuts off with error code 26 displayed in a lockout condition.
6. Thermostat satisfied.
7. Gas valve closes, burner extinguished.
8. Blower post purge for 30 seconds.
Lockout Conditions
The system will go into lock out mode for the following reasons:
1) ERROR CODE 62 or 63
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 display indicates a lockout condition by showing an error code number (62 or 63) with “Service Needed” in the control
display window. Refer to error codes in the diagnostic section of this Service Manual. In a “Soft Lockout” condition, the control
will wait for 60 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 65
If the top of the tank should exceed 200°F, then the high limit control will shut off the burner and the water heater will go into a
“Hard Lockout”. Error code 65 will be shown in the water heater display. The control can only be reset in the “Service
Mode,” which is detailed in the “Troubleshooting” section of this Service Manual.
3) ERROR CODE 29
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 closes, and error code 29 will appear on the control display. When the condition is
corrected, the error code will disappear, and the water heater will resume normal operation. No resetting of the control
display is needed for the pressure switch error code.
4) ERROR CODE 26
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 26 will appear on the display. The lockout condition will reset once the problem is corrected, and the
switch reset. Refer to “Vent Safety Switch Testing and Replacement” in this Service Manual.
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