HVACopediaRheem · Furnace · Ignition
Heating ignition and blower sequence
What happens, in order
- Thermostat calls for heat and the inducer starts on low speed.
- Inducer runs a 30-second pre-purge at low speed.
- Igniter sparks and the gas valve is energized for each ignition trial.
- Furnace makes up to four ignition attempts.
- After burners light, the ECM blower starts on high heat about 15 to 20 seconds later.
- Furnace continues on low fire until the thermostat is satisfied or the heat call is removed.
- When the heat call ends, the inducer runs a post purge and shuts off after 90 seconds (plus slew).
Timings and thresholds
| Item | Value |
|---|---|
| Inducer pre-purge at low speed | 30 seconds |
| Gas valve voltage per ignition trial | 7 seconds |
| Ignition attempts before lockout | 4 attempts |
| Lockout after failed attempts | 1 hour |
| ECM blower start on high heat after burner light | 15-20 seconds |
| Inducer post purge after heat call ends | 90 seconds plus slew |
| Inducer run before fault shutoff (codes 45, 46, 57) | 60 seconds, then off 5 minutes |
Codes you may see during this
Applies to: 96V and 96MDV series 2-stage communicating furnaces
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
- 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
- Heating call sequence of operation (Honeywell integrated control, direct spark ignition) · Heating
Related
Rheem error codes · Rheem tips · Rheem parts · All Rheem sequences
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Source: 96V series installation instructions, p. 121-122. Written in our own words; timings can differ by model and software version, so check the manual for your exact unit.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.