5 Easy Steps to Fixing a Bad Flame Sensor in Your Furnace

October 20, 2022
Furnace in Nacogdoches, TX

The furnace flame sensor was developed to ensure that the gas valve only opens while burning flames. When this does not occur, there is a risk of carbon buildup, which could lead to a fire. With regular use, a coating might form on the metal rod of the flame sensor. This can happen over time and hinder the flow of electric current. The control system of the furnace senses that the burner is faulty and cannot light. It could also cause your furnace to repeatedly start and stop.

The flame sensor is susceptible to corrosion due to the accumulation of carbon from the flame. It could make the sensor stop working. If the burner light goes out a few seconds after turning on the appliance, this is a clear indication that the sensor needs to be cleaned. If you can see the soot coating the sensor, it is time to find a technician who will help you clean it.

Broken or fractured ceramics indicate a problem with the flame sensor, which may require replacement. Below are five steps your technician
will undertake when your furnace flame sensor goes bad.

1. Disconnect the Furnace From the Power Supply

A qualified technician will turn off the power for the furnace as part of safety measures before starting the maintenance. It is not advisable to rely on the thermostat as it does not cut off electricity to the furnace. Instead, using a toggle switch on most devices to disconnect the power supply is a good idea. The technician could also access the circuit-breaker box to shut off the power supply. For gas furnaces, the gas supply line valve will also be turned off prior to doing any work.

2. Locate and Remove the Flame Sensor

Your technician can easily access and remove the flame sensor in your furnace for cleaning. Most furnaces have these on or near the burner unit. Taking precautions, such as turning off the gas to the furnace, is necessary before the access panel can be securely removed.

The actual procedure could vary across devices. For example, your technician might need to slide the access panel to detach it in some devices. In others, it could be necessary to unscrew fasteners or turn retaining knobs to remove the panel. A single one-quarter-inch hex head screw is commonly used to fasten the sensor. One may remove the sensor by unscrewing this. Your technician will also remove the sensor cable for cleaning.

3. Clean the Sensor Gently

After taking out the sensor, the technician will use fine-grit sandpaper to rub the metal rod lightly. The aim is to scrub off the dirt from the sensor. During the process, they will use a fresh paper towel to remove the dust created by the sanding.

4. Connect the Sensor Back to the Furnace

Following the cleaning, your technician will place the flame sensor in its original location, reinstalling the sensor screw and reconnecting the power cable. They will then replace the furnace panel door before turning the electricity and gas back on and testing the system.

Often, the furnace will take a little longer to start up after the flame sensor has been cleaned. You may also observe that the unit’s fan turns on and operates for a short time and then goes off a couple of times before finally kicking on. When everything is done, the system will start working normally, as long as the cleaned sensor isn’t faulty.

5. Flame Sensor Replacement

If the cleaning exercise did not fix the problem, the sensor will need to be replaced. The technician will do this by simply following the steps listed above, minus the cleaning. With a new sensor installed, your furnace should return to normal functioning without continually cutting out.

Get Professional Help

While furnace flame sensor cleaning and replacement is a relatively straightforward task, it’s always best to turn to a professional for help with anything that involves electricity or natural gas. At Nacogdoches Sheet Metal, Plumbing & Air Conditioning, LTD., our highly experienced technicians can provide a range of furnace repair services. We also install and maintain heating and cooling systems and provide indoor air quality solutions. If you have a plumbing problem, our team of plumbers can provide repairs and installations. Our other services include sheet metal fabrication and air duct cleaning. Contact us today for help with your Nacogdoches home’s heating, cooling, and plumbing systems.