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 1 microamp through flame
sense rod to prove flame.
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.
6. Thermostat satisfied.
7. Gas valve closes, burner extinguished.
8. Blower post purge for 30 seconds.
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