Heating call sequence of operation (Honeywell integrated control, direct spark ignition)

What happens, in order

1. On a heat call (W or communicating call), the control checks that both pressure switches are open.
2. The inducer starts a pre-purge at high stage.
3. The air proving (negative pressure) switches, low and high, close.
4. After the 30-second pre-purge, the gas valve opens on high stage for an 8-second ignition trial.
5. The spark igniter fires to light the burners and stays on for up to 7 seconds after the gas valve opens.
6. Eight seconds after the gas valve opens, the flame sensor must prove flame for one second using flame rectification.
7. Twenty seconds after flame is sensed, the gas valve goes to the thermostat demand (low or high). The main blower starts at low or high heat speed to match the demand.
8. When the heat call ends, the gas valve closes and flame goes out. The inducer runs a 10-second post-purge, then stops. The negative pressure switch opens.
9. The main blower runs until its off timing on the integrated control ends.

Timings and thresholds

More Rheem furnace sequences

• Initial startup and lighting (communicating furnace) · Startup
• Gas heat call, direct spark ignition and retry · Ignition
• Gas heat call, hot surface ignition and retry · Ignition
• Gas heat call, ignition and retry (direct spark) · Ignition
• Heating ignition and blower sequence · Ignition
• Retry sequence when burners do not light or flame is not sensed · Ignition
• Two-stage gas heat call, ignition on high fire and retry · Ignition
• Two-stage heat call, high-fire light-off and staging · Ignition