Furnace Ignition Failure (Trane & American Standard)
If your Trane or American Standard gas furnace attempts to start but fails to ignite, the system is shutting down for safety because the ignition sequence is not completing correctly.
What should normally happen
A gas furnace should start the inducer motor, verify airflow, ignite the burners, and then bring on the blower to deliver heat.
Common causes (most likely first)
- Dirty or failed flame sensor ( you will see initial ignition, but it fails after a moment)
- Cracked or weak igniter (no ignition)
- Gas valve not opening
- Pressure switch not closing
- Control board lockout after repeated failures. Error codes normally accompany this.
Safe homeowner checks
- Replace the air filter if dirty or clogged
- Make sure gas supply valves are open, gas is present in tank if propane
- Power cycle the furnace once (turn power off for 30 seconds, then back on)
- Look for diagnostic flash codes on the control board
When this becomes a technician issue
If ignition fails repeatedly or the furnace locks out, electrical testing of the igniter, flame signal, gas valve, and safety circuits is required.
Parts commonly involved
- Air Filter
- Flame sensor
- Igniter
- Gas valve
- Pressure switch
- Furnace control board