HVACopediaRheem · Furnace · Heating
Two-stage heating cycle and staging
What happens, in order
- 24 V signal on W (or a communicating heat message) starts the cycle
- Control checks high and low pressure switches are open
- Inducer starts on high speed for a 30 s pre-purge; pressure switches close as it builds vacuum
- Spark fires and the main valve opens on low fire; ignition control drops out once flame is proven (8 s maximum trial)
- Gas valve stays on low rate through the 20 s warm-up before the blower takes over
- Two-stage thermostat (SW1-3 off) W only = low gas pressure and low blower speed; W2 = high gas pressure and high blower speed
- Single-stage thermostat (SW2-2 and SW2-3 off): low fire for 0 to 7 minutes, then 100 percent firing
- If the call ends during any phase the furnace shuts down at the rate it was running
- Heat call removed furnace returns to the normal off cycle
Timings and thresholds
| Item | Value |
|---|---|
| Pre-purge | 30 s |
| Trial for ignition | 8 s max |
| Warm-up on low rate before blower | 20 s |
| Single-stage thermostat low-to-high timer | 7 min |
Applies to: Rheem RGPE series
Models
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
Related
Rheem error codes · Rheem tips · Rheem parts · All Rheem sequences
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Source: Rheem RGPE series installation manual, Sequence of Operation (Heating Cycle Initiation / Response / Termination). 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.