Among the many issues, you will face with your HVAC system’s gas furnace, the flame sensor will be a regular culprit, often leading to ignition lockout situations. Today, we’ll be looking at how you can determine whether the flame sensor in your gas furnace is preventing a proper startup and how you can remedy the issue.

Usually, if your gas furnace shuts down shortly after turning on, you’re likely looking at a flame sensor fault. Flame sensors check for a fire once the gas furnace starts its ignition process. Without a fire, the gas furnace will continue to buildup gas which could lead to a fire. Therefore, the flame sensor needs to detect the flame during startup to avoid a fire hazard. In many cases, a faulty gas furnace flame sensor is easy to remedy. However, it’s always best to contact HVAC professionals to help you replace or clean the sensor without damaging it or other components.


Flame Sensors Can Wear Out – Understanding What Happened to Your Flame Sensor

Over time, the flame sensor in your gas furnace will wear out. However, if you’re facing ignition issues within a couple of years of buying your HVAC system, it’s likely the cause of the issues is a dirty sensor rather than a worn-out one. The sensors have a low margin of error, and so, if there is dirt or a carbon coating on the sensor, it will not be able to detect the fire. Often, since the gas furnace gets tucked away in a dusty area, the dust accelerates the carbon build up on the sensor and you need to clean it up.


What happens when you have a faulty flame sensor in your gas furnace?

If cleaning does not help restore your gas furnace to a working condition, you need to order a replacement and hire HVAC repair professionals to have a look at your gas furnace. Without a functional flame sensor, your gas furnace will continue to emit gas even when there’s nothing to light it up. This results in a dangerous gas buildup leading to fire hazards.


How to Check If the Flame Sensor in Your Gas Furnace is Damaged?

If you’re unsure as to how to check your flame sensor, follow these easy steps:

  • ·         Shut down your gas furnace
  • ·         Close the gas valve which comes out of the gas furnace
  • ·         Unscrew the mounter
  • ·         Carefully pull out the flame sensor from its housing
  • ·         Check the sensor for damage or dirt
  • ·         If you see any missing pieces or cracks, the sensor needs to be replaced

While replacing a sensor is easy, it’s best if you leave it to your local HVAC professionals, thereby reducing any associated risks. In addition to a sensor replacement, they will conduct some tests to ensure everything is in order.


How Is A Flame Sensor Tested – Remedying Gas Sensor Faults in Your Gas Furnace?

During their maintenance run, the HVAC maintenance experts will thoroughly test your sensor to ensure proper functionality. As the homeowner, you should know what the process entails:

·         They’ll unplug the device and locate the sensor first.

·         Then, using a driver or wrench, they will unfasten the sensor from its housing.

·         Using a multimeter, they’ll check the wires on the sensor to ensure there isn’t a cut off anywhere and the multimeter reads low resistance.

·         Next, to test the sensor, they’ll hold it against a bright but to check if the sensor reads a high resistance, in which case the sensor is working correctly.

·         If there is no change in resistance between the two conditions, the flame sensor will need a replacement. Subsequently, your HVAC contractors will replace it for you.



When your gas furnace repeatedly turns off after starting it up, call in HVAC professionals to check whether the flame sensor is the issue. Once they’ve cleaned or replaced the sensor, your gas furnace should go back to normal operation. In many cases, you can just clean the sensor yourself and restore normal operation, however, it’s best to rely on your local HVAC repair specialists to handle the job for you as they’ll thoroughly test the sensor to ensure everything is normal. Moreover, by hiring professionals, you can rest assured knowing nothing will be damaged and there will be no additional hazards once they’ve completed their job.


See the summary of this content here – How to Check for Damaged Flame Sensor in Gas Furnace [Infographic]

How to Check for Damaged Flame Sensor in Gas Furnace

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