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A flame sensor is a small but essential safety feature on gas furnaces. Keeping it clean allows it to function properly, so it can keep your family safe.

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What Is a Gas Furnace Flame Sensor?

A flame sensor on a gas furnace is a thin metal rod with a porcelain or ceramic insulator on one end, and it ensures that a flame is burning correctly. If there's no flame, the sensor shuts off the gas to avoid leaks, fires or carbon monoxide buildup. It's located within the burner assembly. Keeping it clean ensures the sensor can properly detect flames.

Tools You Need to Clean a Furnace Flame Sensor

Gather your flame sensor cleaning tools before you start to ensure you can complete the job without interruptions. You'll need a screwdriver set to remove the sensor from the furnace. That makes the task easier.

To clean the sensor, use steel wool, an emery cloth, a scouring pad or a cleaning brush. Some people recommend using fine-grit sandpaper, but that could be a little too harsh on the sensor. It could damage the coating on the sensor. Keep a microfiber cloth on hand as well.

How Do You Clean a Dirty Flame Sensor on a Furnace?

Regular cleaning is part of routine furnace flame sensor maintenance. Follow these steps to clean a furnace flame sensor:

• Shut off all power to the furnace, including the gas supply, so you're able to work on the appliance safely.

• Remove the access panel for your furnace to reach the flame sensor.

• Look for the burner assembly to find the rod-like flame sensor. Taking a photo of it will help you remember how the piece is positioned and attached, which can help when you're reassembling it.

• Use a screwdriver to detach the flame sensor from the furnace. Keep track of the screw, so you can reinstall the sensor easily when you're done.

• Rub the selected cleaning tool along the sensor to remove the buildup. The rod should look somewhat shiny when it's clean.

• Go over the sensor one more time with a microfiber cloth to polish it and remove any remaining particles.

• Position the piece back in the burner assembly, the same way it was before. Use the screwdriver to tighten the screw that holds the sensor in place.

• Replace the access panel on the furnace.

• Turn all power sources back on, and restart the furnace to make sure it's working correctly.

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What Happens If You Don't Clean the Flame Sensor?

Debris will continue to build up on your flame sensor if you never clean it. This often interferes with the sensor's ability to detect flames. The sensor might shut off the gas supply, even if the flame is burning properly, which can cause shortcycling (when the furnace shuts off right after it turns on).

In some cases, the dirty sensor could prevent the furnace from lighting properly. If that ignition failure continues, it could go into lockout mode, keeping the furnace from running for several hours.

If your furnace is not heating, troubleshooting it yourself could save you a costly visit from an HVAC contractor. Start by checking the flame sensor. It may just need to be cleaned to get the heater back on track. Fortunately, it's easy to learn how to clean a dirty flame sensor.

How Often Does Flame Sensor Cleaning Need to Be Done?

DIY flame sensor cleaning usually only needs to happen about once per year. However, you may need to clean a furnace flame sensor more often if your home tends to get dusty. Dirt can also build up faster based on the location of the furnace. For example, lint from a nearby laundry room could increase the buildup and require more frequent cleaning.

Watch for signs that the flame sensor needs to be cleaned, including:

• The furnace turning off and on quickly without fully warming up the home

• Cool air coming from the vents

• A yellow or orange flame

• Error codes related to ignition or flame signal problems

• Visible buildup on the sensor

If cleaning doesn't resolve the issues, the flame sensor could be bad. The component typically lasts for five to 10 years, but it could fail sooner if you never clean it or if you damage it during cleaning.