Furnace Keeps Shutting Off
Quick Answer
A furnace that keeps shutting off is usually overheating due to a dirty air filter or blocked vents. Replace the filter and ensure all vents are open. If that doesn't help, the flame sensor may need cleaning or the limit switch may be faulty.
Safe Checks You Can Do
- 1Replace air filter - The #1 cause of overheating and shutdown. Replace immediately if dirty.
- 2Open all vents - Closed or blocked vents restrict airflow and cause overheating.
- 3Check exhaust vent - Look outside for blockages in the exhaust pipe.
- 4Reset the system - Turn off for 5 minutes at thermostat, then restart.
Likely Causes
- Dirty air filter
Restricts airflow, causing the heat exchanger to overheat and trigger safety shutdown.
- Dirty flame sensor
Can't detect the burner flame, causing gas valve to close shortly after ignition.
- Faulty limit switch
The limit switch may be incorrectly sensing overheating or may be worn out.
- Blocked exhaust
A blocked flue prevents proper venting, triggering pressure switch shutdown.
- Draft inducer motor
A failing inducer motor can't maintain proper exhaust, causing shutdown.
When to Call a Pro
- Filter replacement and reset don't solve the problem
- Furnace shows error codes on display
- You hear the furnace ignite then immediately shut off
- Problem happens more than 3 times in an hour
- You notice any unusual smells or sounds