Two-stage gas heat call, ignition on high fire and retry

What happens, in order

1. Thermostat W closes (or a communicating thermostat sends a heat call); control checks that both pressure switches are open
2. Inducer starts on high speed for pre-purge
3. Low and high pressure switches close
4. After the 30 s pre-purge the gas valve opens on high stage for the 8 s trial for ignition
5. Spark stays on for up to 7 s
6. Flame sensor must prove flame for 1 s at the 8 s mark
7. If the burners do not light the control repeats the ignition sequence, up to 4 times, then goes to a 1 hour lockout
8. 20 s after flame the gas valve moves to the stage the thermostat is asking for (no change if high stage is called); blower starts at the matching low or high heat speed
9. Call for heat ends valve closes, flame goes out, inducer runs a 10 s post-purge and the pressure switch opens
10. Main blower runs out the heat off delay set on the board

Timings and thresholds

Models

More Rheem furnace sequences

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• Heating ignition and blower sequence · Ignition
• Retry sequence when burners do not light or flame is not sensed · Ignition
• Two-stage heat call, high-fire light-off and staging · Ignition
• Heating call sequence of operation (Honeywell integrated control, direct spark ignition) · Heating