HVACopediaTrane · Furnace · Heating
Heating sequence of operation
What happens, in order
- Thermostat calls for heat and R and W contacts close.
- Control runs its self-check and confirms pressure switch contacts are open and limit switch contacts are closed.
- Induced draft blower energizes.
- As the draft blower reaches speed, the pressure switch closes and the ignitor warm-up begins.
- Ignitor heats, then the gas valve opens to feed the burners.
- Flame sensor confirms ignition within a 4 second trial period.
- Fan-on delay times out and the indoor blower starts.
- On thermostat satisfied, gas valve closes, flame goes out and the draft blower stops.
- Indoor blower runs through the fan-off period, then the control shuts it off.
Timings and thresholds
| Item | Value |
|---|---|
| Ignitor warm-up before gas valve opens | approx. 20 s |
| Flame sensor ignition trial | 4 s |
| Blower ON delay (upflow/horizontal) | approx. 45 s |
| Blower ON delay (downflow) | 10 s |
| Fan-off period | 60, 100, 140 or 180 s (factory 100 s) |
Codes you may see during this
Applies to: AUH1B furnaces
More Trane furnace sequences
- First-stage gas heating · Heating
- Heating call sequence of operation · Heating
- Second-stage gas heating (S8X2 only) · Heating
- Cooling and heat pump calls on S8 furnace control · Cooling
- Cooling fan-off delay · Cooling
Related
Trane error codes · Trane tips · Trane parts · All Trane sequences
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Source: Trane installer's manual (AUH1B040A9241A), p. 40. 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.