If your furnace fires up and then shuts off a few seconds later, a dirty flame sensor is a common and fixable cause. This is one of the few furnace jobs a careful homeowner can do safely. Here’s how, in six steps.
What the Flame Sensor Does
The flame sensor is a thin metal rod sitting in the burner flame. Its job is to confirm a flame is actually present. When it gets coated in carbon buildup, it can’t sense the flame, so the furnace shuts off the gas as a safety measure, which reads as that quick on-then-off behavior.
How to Clean It, Step by Step
- 1. Cut the power. Turn the furnace off at the switch and the breaker. Shut off the gas valve too.
- 2. Find and remove the sensor. It’s usually a small rod held by a single screw near the burners. Note how it sits, then remove the screw and gently pull it out.
- 3. Inspect it. You’ll likely see a dull or sooty coating on the metal rod.
- 4. Clean it gently. Use fine steel wool or light sandpaper to lightly scuff off the buildup. Don’t scrub hard; you just want it clean and shiny.
- 5. Wipe it down. Remove any residue with a clean cloth.
- 6. Reinstall and restore power. Screw it back in, turn the gas, breaker, and furnace back on, and test.
When to Call a Pro
If cleaning the sensor doesn’t fix the short cycling, or you’re not comfortable working around the gas components, leave it to a technician. Everything beyond the flame sensor should be left to a pro anyway. Bearcat can handle it. See our heating repair services, or call (509) 891-5110.
