Furnace Flame Sensor: The Cheap Fix for Short-Cycling
A dirty flame sensor is one of the most common — and inexpensive — causes of a furnace that fires then shuts off.
If your furnace ignites then shuts down seconds later, a dirty flame sensor is often the culprit — a quick, low-cost fix during service.
What the flame sensor does
The flame sensor confirms the burners have lit. When it gets coated with residue, it can't 'see' the flame, so the furnace shuts the gas off as a safety measure — causing repeated cycling.
The fix
A technician removes and gently cleans the sensor (or replaces it if worn) during a tune-up, restoring reliable ignition. It's one of the most common, inexpensive furnace repairs.
Key takeaways
- Fires then quits = suspect the flame sensor
- Cleaning is quick and inexpensive
- Often resolved during annual servicing
- Don't bypass the safety — clean the sensor
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