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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 1.0 microamp through flame sense
rod to prove flame.
c. If the blocked vent safety switch contacts (normally closed) opens, then the ignition sequence will not
start and an error code 67 (Vent safety switch failed to close/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 safety switch opens, the gas valve closes, the blower continues to
operate indefinitely and error code 67 will be displayed after a couple minutes (up to 5 minutes) with
“Service Needed.”
6. Thermostat satisfied.
7. Gas valve closes, burner extinguished.
8. Blower post purge for 30 seconds.
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