HVACopediaTrane · Furnace · Heating
First-stage gas heating
What happens, in order
- Thermostat R-W1 closes and 24 V arrives at the W1 terminal; the display shows Xt (S8B1/S8X1) or Xt1 (S8X2)
- Control self-checks and sends 24 V out the HLO terminal to confirm the rollout switches, main limit and any reverse airflow switches are closed
- Control confirms pressure switch 1 (and 2 on S8X2) is open
- Inducer relay closes and the inducer starts; S8X2 starts it on high speed for about 6 seconds, then low
- Pressure switch 1 must close; if it has not closed in 60 seconds the control declares an e3.1 error and runs the inducer on high to try to close it
- Ignitor relay closes and the ignitor warms for about 17 seconds
- First-stage gas valve opens; flame must be proven within 4 seconds
- Flame proven the blower heat on-delay timer runs, then the blower starts at first-stage speed
- Thermostat satisfied gas valve closes, inducer runs about 5 seconds, and the blower runs for the blower off time set in the control menu
- Display returns to IDL
Timings and thresholds
| Item | Value |
|---|---|
| Ignitor warm-up | about 17 s |
| Flame prove time | 4 s |
| Pressure switch 1 prove time | 60 s |
| Post-purge | about 5 s |
| Typical flame current | 0.75 to 3.0 uA (read as 0.75 to 3 VDC at the FP pads) |
| EAC relay delay | about 2 s after blower starts |
| HUM relay delay | about 1 s after blower starts |
Codes you may see during this
Applies to: S8B1, S8X1 and S8X2 80 percent furnaces
Models
More Trane furnace sequences
- Heating call sequence of operation · Heating
- Heating 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
Take it to the job
Sequences of operation, error codes and tips work offline in the HVACopedia app.
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.