HVACopediaKeepRite · Furnace · Ignition
Modulating 95% furnace: ignition sequence and retries
What happens, in order
- Thermostat closes R-W; control self-checks and confirms the low, medium and high pressure switches are open
- Inducer ramps up slowly; after the low and then the medium pressure switch close, the control records the inducer RPM to judge vent resistance, and a 25 s prepurge starts
- Hot surface igniter warms for 17 s
- Gas valve opens; flame proving starts 5 s later and lasts 2 s
- Flame proven inducer speed is trimmed slightly down if the cycle started at intermediate heat, or increased if it started at maximum heat
- No flame in 2 s gas valve closes and the control repeats the sequence up to 3 more times before ignition lockout; auto reset after 3 hours or by interrupting power
- Flame seen when it should be off control locks out gas heating and runs the inducer at full speed until flame is gone
Timings and thresholds
| Item | Value |
|---|---|
| Prepurge | 25 s |
| Igniter warm-up | 17 s |
| Flame proving | 2 s |
| Ignition trials | 4 total |
| Lockout auto-reset | 3 hours |
Applies to: ICP (F-G)9MAE modulating 95% furnace
Models
G9MAE0601714A
More KeepRite furnace sequences
- Single- and two-stage 95% furnace: ignition sequence and retries · Ignition
- Modulating 95% furnace: adaptive heating, staging and blower delays · Heating
- Single-stage 95% furnace: heating cycle and blower delays · Heating
- Two-stage 95% furnace: low/high heat, staging and blower delays · Heating
- Furnace blower with outdoor A/C: cooling, dehumidify and continuous fan · Cooling
- Furnace used with a heat pump (dual fuel blower timing) · Other
Take it to the job
Sequences of operation, error codes and tips work offline in the HVACopedia app.
Source: ICP (F-G)9MAE service manual 440 04 4700 00, Sequence of Operation. 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.