how to clean flame sensor

How to Clean a Flame Sensor on Furnace

Before the cold weather kicks in, it is imperative to ensure that your furnace is in perfect working condition. Without this heat source for your home, the chilly weather can ruin your home’s comfort. 

One small device that can ruin that winter comfort is a furnace flame sensor. While it’s quite a small part of the furnace, a defective or dirty flame sensor can make your furnace stop working.

Therefore, if you notice that your furnace unexpectedly stops after it starts or it doesn’t generate heat at all, the flame sensor could be the cause. But do you know how to clean a flame sensor on a gas furnace? This article shows you exactly how.

But first,

What Does a Furnace Flame Sensor Do?

The work of a flame sensor is simple – detect flame in a furnace. And when it doesn’t, it shuts down your entire heating system.

Generally, the flame sensor helps to ensure that whenever the gas valve opens to release gas, the furnace igniter does its work. If the igniter can’t ignite this gas, the sensor alerts the control board, which subsequently closes the gas valve by shutting off the voltage.

This helps to prevent gas buildup in the furnace and subsequently to the surroundings.

If your furnace keeps shutting down after starting, you might need to check your flame sensor, especially if the igniter is working well. Sometimes, the flame might be present, but the sensor is faulty or just dirty.

In this case, the flame sensor doesn’t detect the flame and assumes that the igniter isn’t working. If this happens, the sensor will keep triggering the gas valve to close, thus shutting down your HVAC system.

Flame sensor cleaning might be all you need to restore the furnace operations.

What Makes the Flame Sensor Dirty?

Most of the time, the flame sensor is not faulty but only dirty. A dirty flame sensor is mainly due to carbon buildup.

As dirt sticks on the sensor rod and burns up, this results in carbon buildup. And since the sensor has to be quite sensitive to detect the flame, even the slightest carbon buildup affects its functions.

For this reason, if you suspect that this is the case, remove the sensor rod, clean it, and put it back.

How to Clean a Flame Sensor 

While most HVAC repair and maintenance tasks are complicated and require an expert, furnace flame sensor cleaning isn’t. You can easily complete this task without calling an HVAC technician.

You can learn how to clean a flame sensor in these simple steps:

1. Turn off the Furnace

Shutting off the power to your furnace is the first step. You will achieve this by switching the toggle switch, usually located next to or on the furnace, to an off position. Alternatively, you can access the circuit-breaker box and shut down the furnace from there.

Note: Your furnace will not shut down by turning off your thermostat.

Also, manually shutting off the gas will be necessary for homeowners with gas valves that are not electrically controlled.

2. Access and Remove the Furnace Flame Sensor

Flame sensors for most furnaces are quite accessible and easy to remove. They are usually located on or next to the burner assembly of your furnace.

After ensuring the furnace and gas supply are off, you can go on and safely remove the access panel. This will depend on the model of your furnace.

In some units, you need to slide the access panel to detach. Others have the panel fixed with screws or retaining knobs that you must unscrew.

The sensor is typically secured by a single ¼-inch hex head screw. By unscrewing this, you can slide the sensor out. Sometimes, you might need to disconnect the cable from the sensor to allow easier cleaning.

3. Clean your Flame Sensor

After you have detached the flame sensor, it’s now time to clean it.

First, you need to have grit sandpaper or steel wool. Use it to gently rub the flame rod sensor to remove any carbon buildup. Ensure that you do it gently.

After this, wipe the rod with a paper towel to remove the dust from the sanding. Also, check if the power wire is corroded and clean it.

4. Reconnect the Flame Sensor

Just as you removed it, secure back the flame sensor with a screw. And, if you disconnected the power cable, reconnect that first before mounting back the sensor.

After this, put back the access panel to close the furnace. Turn the power on to test whether the furnace is now working.

If it takes a few seconds more to start than you are used to, don’t worry. This can happen after cleaning up the flame sensor. In some cases, the fan kicks in and runs for a while as the unit goes through the checks. After this, the system is back again.

If the problem doesn’t go away, then you know that your flame sensor is defective and requires replacing.   

How to Replace a Faulty Sensor

To replace the defective flame sensor, you need to follow the same procedure. However, instead of cleaning, you replace the sensor with a new one.

But before you buy a new sensor, it might help to first contact an HVAC expert to inspect and diagnose the problem. Remember, there are other issues that might be causing the problem. You don’t want to buy a new flame sensor only to find out it’s still not the issue.

Key Takeaway

Furnace maintenance is crucial to ensure that your heating system works properly. As you have noticed, even a small device like the flame sensor can cause disruptions to your HVAC system’s functions.

For this reason, make sure you schedule regular maintenance by a professional HVAC technician. This will help guarantee that your home is the best place to be during the cold season.

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