Furnace Ignition Lockout: The Causes and Solutions

The ignition lockout is when the flame sensor identifies unsafe conditions or security threats, and the controller immediately shuts down the furnace. There are many reasons behind the furnace ignition lockout. If you live near Diamond Spring and are searching for a ‘furnace repair near me‘, contact Essential Air Heating and Air Conditioning for assistance.

In the meantime, continue reading this post for more detailed information on the causes and solutions behind furnace Ignition Lockout.

Common Reasons Behind Furnace Ignition Lockout

There are two types of furnace ignite lockouts: soft lockout and hard lockout. When the furnace stops suddenly, an individual can restart it two times after the shutdown. The hard lockout is when the furnace unit does not start even after three consecutive trials.

You may encounter this problem for three reasons:

1. Defective Flame Sensor

A defective sensor is one of the most common reasons behind furnace lockouts. If the sensor is faulty or dirty and needs a replacement, it will lose the power to detect the flame. As a result, the controller will stop the ignition sequence, resulting in an ignition lockout.

2. Faulty igniter

The igniter will not light the pilot flame when it is faulty. When the furnace igniter does not activate within a few seconds, the sensor won’t be able to detect the flame. As a result, the controller will automatically stop responding, resulting in an ignition lockout. Therefore, constant failure is another primary reason for ignition lockout.

3. Limit switch problems

The primary role of a limit switch is to monitor the temperature of the heat exchanger. Additionally, it determines the pressure of the fuel. The limit switch will shut down if the temperature is too high or low. Then, the furnace will enter lockout mode. The dirty filter trips the limit switch, further lowering the airflow and leading to an ignition lockout.

Practical Solutions For The Furnace Ignition Lockout

Here are a few solutions for furnace ignition lockout:

  • Replace the air filter to avoid the limit switch tripping.
  • A dirty flame sensor can also be the reason behind this problem. You can unscrew the flame sensor to clean the sensor with the scouring pad. You must not use your hands to clean them.
  • You also must clean the vent pipes with the filters. Often a blockage appears in the PVC vent pipes when there is excessive dirt. As a result, the dirt will clog the pipe and lead to the furnace lockout problem.
  • Poorly sloped PVC vent pipes sometimes accumulate dirt or dust particles and debris. In such a scenario, you must clean the vent pipe using a vacuum cleaner.
  • To prevent the ignition lockout, you must schedule furnace service at least two times every year.


Furnace ignition lockout is one of the common problems that many people face. Now that you know all the possible reasons and solutions for furnace ignition lockout, it will be easy for you to identify the problem and solve them.

If you live in the area and are looking for expert furnace repair in Diamond Springs, you can opt for the services of Essential Air Heating & Air Conditioning Specialists. We take pride in providing the best heating and cooling services.