How To Clean A Furnace Flame Sensor: The Complete Guide

flame sensor is one of the most essential parts of a furnace. It is not only designed to make your furnace work but also to keep it safe. A furnace flame sensor works to regulate the flow of gas coming into your furnace and automatically shuts down the unit if the gas burners do not light as to prevent gas build-up or worse, gas poisoning or catastrophic explosion. Most commonly, these automatic shutdowns are done three times before a “safety lockout” for an hour is done to dissipate the initial gas build-up before it is safe to be turned on again.

Most often than not, if your flame sensor experiences problems, it is not broken, but just dirty. A furnace flame sensor must be kept in a proper and clean state at all times for it to perform well and not give you even bigger furnace problems like your furnace shutting off intermittently. The constant inability of your furnace to start will not only leave your homes cold but can also cause major problems like reduce efficiency to some parts of your furnace, and worse, totally breaks your furnace unit down.

What Makes Flame Sensors Dirty?

How To Clean A Furnace Flame Sensor: The Complete Guide 1

Carbon Buildup. Furnaces are usually located in home areas where there are lots of dust in the air. Since flame sensors are in flame most of the time, dust and other particles can easily burn to it and cause corrosion and carbon buildup over time. This can lead to sensing errors that will dictate your furnace to shut down every time you turn it on.

A dirty flame sensor is easily detectable. The most common sign of a sensor issue is when your furnace gas burners light up then go out after a few seconds. However, when you see gunks/ discoloration at the sensor’s tip, it also calls for a cleanup.

Doing a regular check-up for dirt and carbon build-ups on your furnace flame sensors can improve not only its efficiency but for your furnace’s as well.

Things You Need To Clean Flame Sensors

A dirty flame sensor is a very common issue every homeowner faces with their furnace. The good news is, it is not hard to maintain a flame sensor at all. It is a very easy job and you can easily do it yourself with the help of some of the common repair tools you can easily find at your home.

  • ¼” hex driver or wrench, but may vary depending on your mounting screw type
  • Small piece of light grit sandpaper, steel wool, or emery cloth
  • Paper towel

Cleaning a Furnace Flame Sensor Step-by-step Guide

    1. Shut the Furnace Off

    Whenever you do any HVAC unit or part (or any appliance per se) repair or clean-up, you must ALWAYS turn the unit off.

    You can switch it off through the toggle switch on/near your furnace or through its dedicated circuit breaker box, in the absence of a switch.

    * NOTE: Make sure to shut off MAIN POWER, and not the thermostat alone.

    Also, if your gas valve is not electrically controlled, shut off the gas unit as well.

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2.Remove the Flame Sensor

Locate a thin metallic rod-like part usually at the back of the furnace and in the path of the burner. 

The flame sensors are typically kept in place by one or two ¼” hex head screws. Simply, take the screws out and carefully slide the sensors out from the burner bracket or assembly.

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3. Clean the Sensor

For some units, you may have to detach the wires that are connecting to the sensor so you can clean it well. This is not necessary but detaching the wires will give you ample space and flexibility in cleaning the sensor later on.

To clean the sensor, simply rub the metal rod gently with light grit sandpaper, steel wool, or emery cloth to get rid of the carbon buildup.

* Note: Never use sandpaper as it will damage your flame sensor’s rod.

After that, use a clean and dry paper towel to get the excess particles and dust from the metal rod.

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4. Put the Sensor Back

If you detached wires leading to the flame sensor, just reconnect it. Then, mount the sensor back to the burner bracket or assembly by putting back the hex screw/s.

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5. Check if the Furnace Now Works Properly

Now, turn the furnace back on. Wait for a few seconds as the furnace may not immediately start and may still be resetting and doing some start-up checks. Upon startup, your furnace unit must operate normally and stays on until an automatic shut off is commanded by the thermostat. Make sure to leave your furnace on for even one cycle to make sure the problem does not persist.

Furnace Flame Sensor Replacement

If you followed the steps above and your furnace still shuts off abruptly after turning it on, then your furnace flame sensor may be faulty and needs to be replaced.

To replace your flame sensor, simply redo the steps above (skipping the cleaning part), and replacing it with a new sensor. In replacing your flame sensor, make sure to purchase the correct part replacement.

ACEHVACPARTS offers a broad list of furnace replacement flame sensor that you can choose from. If you’re not sure which part to get, please feel free to contact us with your model and serial number so we can suggest the best match for your unit.

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