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by Rifat A. in Blog 0 comment

Does your gas furnace continuously shut down after each startup and stop responding within a few minutes? If you answered yes, your gas furnace is likely in ignition lockout and will require a proper reset or additional repair work.

Modern furnaces are well-equipped with several safety measures. Therefore, your gas furnace comes with several sensors to keep the unit in check and ensure proper functionality. As a result, when one of these sensors detects an anomaly or unsafe condition within the gas furnace, the furnace controllers force a shut down immediately to prevent damage and maintain safety. With repeated resets, the gas furnace goes into ignition lockout. And so, in most cases, unless you get a trained HVAC specialist to have a look at your system, amend the sensors and force a reset, the gas furnace will continue to malfunction.


What is a furnace ignition lockout?

When the sensors in your HVAC system’s gas furnace detect an unsafe condition during startup, it will force it to shut down to avoid causing any damage. This is known as an ignition lockout, wherein the sensors prevent the furnace from turning on at all. Although there are a few reasons why your gas furnace can reach this invalid state, the outcome is that you’re in a furnace ignition lockout and will remain in that state until you force a reset. A total lockout occurs when homeowners try to turn the gas furnace several times despite the sensors detecting a potential hazard.


What are the Causes of a Furnace Ignition Lockout?

Among the many sensors in your gas furnace, when faced with an ignition lockout, the usual culprits are the flame sensors, ignitors, and limit switches.

1.      Defective Flame Sensor

A defective flame sensor is a prime suspect when it comes to a furnace ignition lockout. Here, the sensor is responsible for checking if there is a fire once the furnace starts up. Therefore, if the sensor malfunctions, it won’t detect the flame. Subsequently, the controller will kick in and prevent the gas furnace from completing the ignition process. Modern furnaces allow the ignition process to fail at most twice before sending the system into a lockout state.

2.      Faulty Igniter

A faulty igniter is one of the common culprits when you’re facing a furnace ignition lockout in your HVAC system. If the igniter isn’t functioning properly, the flame sensor will not detect the fire within the first few seconds of start-up, and subsequently shut the machine down. After a few retries, the furnace will go into lockout. If your gas furnace has a pilot light instead of an igniter, it might still send the system into a lockout.

3.      Limit Switch

Dirty air filters attached to your gas furnace can also trigger an ignition lockout. In this case, a limit switch that monitors fuel and air pressure gets tripped due to poor airflow and circulation. Although this is harder to spot, modern HVAC systems come with status lights which indicate which sensor is failing during a failed ignition.


Troubleshooting a Furnace Ignition Lockout

Hire an HVAC professional to help with your gas furnace ignition lockout issue, the common remedies are:

  • Clean or replace the flame sensor entirely. This requires a proper inspection for cracks and signs of damage.
  • Clean or replace the air filter. This will prevent the limit switch from sending the gas furnace into a lockout state. Once the air filter is replaced, and the air supply is adequate, your limit switch will return to normal expected operation.
  • Clean out your pipes and vents. Blockages and other obstructions in the pipes will lead to more trouble.



Regardless of how you got into a furnace ignition lockout, a reset is mandatory. The best way to reset your furnace is to power it off and on again after about half an hour. If that does not work, you will have to get in touch with HVAC maintenance professionals and follow their instructions from there. To ensure safety, they will perform some mandatory tests before getting your furnace out of the lockout. Therefore, resetting your gas furnace is easy if you hire the right HVAC contractors to take care of the job. Once they identify the culprit, they’ll remedy the issue quickly.


See the summary of this article here – 3 Causes of a Furnace Ignition Lockout [Infographic]

3 Causes of a Furnace Ignition Lockout
3 Causes of a Furnace Ignition Lockout

By the way, are you looking for an HVAC system for your home?

Check out Green Leaf Air Store where we have a wide range of residential & commercial HVAC system including: –

Complete Goodman HVAC SystemComplete Trane HVAC systemHeat PumpsAir HandlersGas Furnaces

Besides, for any Air Duct Cleaning, AC installation, AC replacement and AC repair services, call Green Leaf Air to ensure you get the best quotes and satisfying service.

Rifat A.

HVAC Expert, Author & Mathematician... rifatahmed.com

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