How to Clean a Flame Sensor on a Furnace –6 Easy Steps

Has your furnace been shutting down right after you start it up? It’s evidence that it is malfunctioning, but what could be the issue? One of the reasons your furnace could be having this manner so that it has a dirty flame sensor.

If there is one, the upside of this problem is that you can clean it yourself without involving an expert. Note that you must leave all other maintenance and repair works on your furnace to a furnace expert, but for this part, you should do it by all means.

Besides knowing how to clean a flame sensor in a furnace, it’s also easy to determine if it is the source of the problem, especially when working with a gas furnace.

Before looking at the steps you should take when cleaning a flame sensor, it’s essential to know what it is and how it works.

What a Flame Sensor Is and Its Mode of Operation

Understanding its nature is essential to learning how to clean a flame sensor on a furnace. A flame sensor is a thin metallic rod usually bent and located inside a furnace at the burner assembly and in front of the flame stream.

The sensor is a coordinator between an open gas valve and the fire. It reflects the flame the instance the burners ignite. The sensor shuts the unit down if the gas is running but can’t detect a flame. Look at it as a safety design that can act up to three times.

After the third time, your system would shut down, allowing you to try the ignition again in about an hour. Operating a furnace without knowing that the flame sensor is dirty would cause damage to other parts, not to mention you would be in the cold.

How Does a Flame Sensor Get Dirty

Another essential thing to know before embarking on the actual flame sensor cleaning is how it gets dirty. You need not run to replace the flame sensor when it fails to work, as it could be because it’s dirty from carbon buildup.

It’s a pretty sensitive part, so the slightest amount of carbon coating will cause it to shut down. Typically due to a furnace’s location in a home, you’ll likely experience this issue from time to time. The good news is that cleansing only takes about six easy steps.

4 Easy Steps on How to Clean Flame Sensor on Furnace

Ensure you follow every step to the minor details to get the best results.

Step 1: Gather Your Tools

First, you must assemble all the necessary tools to get the job done. Ensure you keep the tools you need near and handy to avoid reaching out unnecessarily. You will require the following:

  • A ¼ “hex driver or wrench

  • Light grit sandpaper/steel wool /emery cloth

  • Dry paper towel

Step 2: Shut Off the Power to the Unit

Once you have all the tools, you can start by shutting off the power to the unit and not just the thermostat. Look for a toggle switch on the unit or near it. Go ahead and sit the power at the circuit breaker box if you can’t find the switch.

Every furnace has a dedicated circuit breaker that shuts the system down. Ensure that you understand all the relevant parts of your furnace before starting.

Step 3: Take Out the Flame Sensor

When it’s time to take out the sensor, you will find it easily accessible. Find it mounted by a single ¼ “head screw. Use the hex driver to unscrew it. The sensor slides out immediately to a position that will make cleaning easy.

Be cautious when removing the sensor. Go ahead and detach it from the wire at the end if you need additional space to work.

Step 4: Clean the Sensor

Get the light grit sandpaper and start rubbing the metal rod gently? Your goal is only to remove the buildup of the sensor and not give it a serious scrub. Wipe the dust away using a clean paper towel after rubbing the metal rod.

Step 5: Place the Sensor Back In

Once you clean, it’s time to put the sensor back in position. Start by reconnecting the wire. Next, remount the sensor on the assembly runner and screw it with the ¼ “hex screw. Finally, replace the unit’s doors and turn the power on to start working.

Step 6: Run Diagnostics on the Unit

After a few seconds, the unit should start, including the fans. It’s normal for the furnace to run a short series of checks before starting since you had cut off its power.

You don’t have to do much else from there as the thermostat takes over. Switch the on and off one more time to ensure it works correctly before celebrating your success.

Flame Sensor Cleaning On a Gas Furnace

When cleansing a gas furnace, you might find that it lacks electric controls, such as the toggle switch. If it does have these controls, complete the procedure described above and switch off the power. If there is no switch, you must shut off the gas supply to the unit first before starting to work on it.

The first part of how to clean the flame sensor on a gas furnace is blowing the dust off using your mouth or blowers. It might have stubborn stains and dust, so you have to use a toothbrush to scrub the stubborn stains. Follow the steps described above from there.

Final Words

Knowing how to clean a flame sensor on a furnace is easy since the steps involved are straightforward. Please don’t rush to claim that you have a dead furnace when it shuts down since the problem could be a dirty flame sensor. Note that the sensor is fragile.

If you run the system after cleansing the sensor and it doesn’t start, you might have a broken sensor in your hand. The sensor is probably broken and not dirty, and the only option is to replace it. Follow the steps described above but don’t use sandpaper.

Contact a heating contractor to discover the problem if your system can’t start running.

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