York / Coleman Gas Furnace Sequence of Operation Flow Chart

• Thermostat calls for heat ↓

• Inducer motor starts (establishes draft) ↓

• Pressure switch proves draft (safety check) ↓

• Ignition sequence begins (hot surface ignitor or spark) ↓

• Gas valve opens ↓

• Burner ignition ↓

• Flame sensor proves flame ↓

• Blower motor starts after delay ↓

• Furnace runs until thermostat is satisfied ↓

• Gas valve closes & burners shut off ↓

• Blower runs post‑purge (clears residual heat/gases) ↓

• Blower shuts off → Cycle complete

If at any point the furnace quits during operation the first thing to check is the control board to see if there are any LED lights blinking on it --> See Flash Code Chart