Why Does My Furnace Keep Shutting Off?

Is your furnace having trouble staying on once it fires up? Does it quickly shut off after you start it, repeating this cycle before fully shutting down? Many homeowners experience this issue annually, often due to a dirty flame sensor.

While heating, ventilation, and air conditioning repairs can be complex, cleaning the flame sensor is a simple task that you can do yourself. This example focuses on a gas-fired furnace, but flame sensors are found in boilers and other gas-burning appliances as well.

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What Is a Flame Sensor and What Does It Do?

A flame sensor, a thin, bent metallic rod located at the burner assembly, confirms the presence of fire in your furnace when the gas valve is open. Its purpose is to prevent the emission of unignited gas, thereby averting potential hazards.

At startup, if a flame isn't detected within a short period, your furnace will automatically shut down. This cycle may repeat up to three times, leading to an hour-long safety lockout. This not only leaves you without heat but also wears down furnace components, reducing efficiency and lifespan.

What Causes a Flame Sensor to Get Dirty?

Carbon buildup on the flame sensor can cause malfunctions. Located in areas prone to debris accumulation, such as basements and attics, these sensors accumulate carbon and dirt over time.

What You Need to Make the Repair:

* 1/4” Hex Driver or Wrench (may vary based on mounting screw type)
* Small piece of light-grit sandpaper, steel wool, or emery cloth
* Dry and Clean Paper Towel

How to Make the Repair
Follow these steps to clean your furnace flame rod sensor:

1) Power Shut Off Examples
Before beginning any repairs, shut off the power to your furnace. Locate and toggle the furnace's light switch or use the breaker panel to cut off power. Ensure safety by turning off the gas valve if applicable.

2) Remove the Sensor
Unscrew the sensor, typically mounted with a 1/4” hex head screw, and gently detach it.

3) Clean the Sensor
Lightly sand the metal rod to remove carbon buildup. Wipe the sensor clean with a dry paper towel.

4) Replace the Sensor
Reconnect the wire (if detached), remount the sensor, and tighten the screw. Restore power to the furnace.

5) Check Your Results
Ensure the unit operates smoothly and maintains a flame. If issues persist, contact a professional technician.

How to Replace a Broken Flame Sensor
If cleaning doesn't resolve the issue, replace the sensor using similar steps. Contact a technician if problems persist.

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