HVACopediaTrane · Furnace · Heating
Second-stage gas heating (S8X2 only)
What happens, in order
- Second stage cannot run without first stage
- Thermostat R-W2 closes and 24 V arrives at W2; display shows Ht2 then Xt2
- Control checks pressure switch 2 is open, then energizes the second-stage inducer relay and runs the inducer on high speed
- Second-stage gas valve relay closes and the blower ramps to second-stage heating speed
- Control watches pressure switch 2; if it has not closed in 45 seconds a PS2 open error is declared and the furnace stays on first stage
- After a PS2 failure the control waits 10 minutes and tries again; after the third failed try in the same call it stays on first stage until R-W2 opens
- W2 satisfied second-stage valve closes and the blower ramps down to first-stage speed
- W1 satisfied gas valve closes, inducer post-purge, blower off time
Timings and thresholds
| Item | Value |
|---|---|
| Pressure switch 2 prove time | 45 s |
| Retry wait after PS2 failure | 10 min |
| Attempts per call | 3 |
Codes you may see during this
PS2 open error
Applies to: S8X2 two-stage furnaces
Models
More Trane furnace sequences
- First-stage gas heating · Heating
- Heating call sequence of operation · Heating
- Heating sequence of operation · Heating
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- Cooling fan-off delay · Cooling
Related
Trane error codes · Trane tips · Trane parts · All Trane sequences
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Source: Trane S8B1/S8X1/S8X2 installation 18-CE14D1-1A-EN, Sequence of Operation pp.59-61. 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.