Furnace heating cycle

What happens, in order

1. Thermostat calls for heat (R to W) with fan on AUTO
2. Pressure switch must be open at the start of the cycle, then closes when the inducer provides enough combustion air
3. Ignitor warms for 17 seconds
4. Gas valve opens and ignition occurs; the flame sensor takes over
5. Blower starts 30 seconds after the gas valve opens if flame is detected, on the speed selected on the HEAT tap
6. Normal operation continues until R and W open
7. Thermostat satisfied gas valve and ignitor drop, the vent motor runs 15 seconds, and the blower runs for the BLOWER OFF DELAY setting
8. Limit open control runs supply blower and inducer; open over 5 minutes goes to hard lockout (11 red flashes); open over 15 minutes is read as a tripped rollout (5 red flashes)
9. Limit opening five times in one call gives 4 red flashes and a one hour soft lockout

Timings and thresholds

Codes you may see during this

Slow green flash normal, slow amber flash call for heat; 4 amber (Y without G); continuous amber (low flame); 1 to 11 and 13 red flashes

Models

More York furnace sequences

• Furnace ignition retry and lockout · Ignition