Home / Blog / Furnance Services / Furnace Ignition Lockout: Causes & Solution

The heating process of your furnace system begins with the ignition. The ignitor is responsible for lighting the pilot flame that leads to the rest of the furnace functioning. If the ignition fails, you will experience cool air flow, short cycling, circuit breaker tripping, and many other furnace malfunctions.

There are many causes for the furnace ignition lockout. Let’s go through the causes of ignition lockout to apply the right solution to the problem.

If you happen to live in Fairfax or the surrounding areas and need professional assistance with your furnace, contact AVS Heating and Air Conditioning for quality furnace service.

Causes for Furnace Ignition Lockout

The flame sensor detects security threats or unsafe conditions, and the controller shuts down the furnace. This is called ignition lockout.
The furnace ignition lockout obstructs the furnace’s performance. There are two kinds of furnace ignition lockouts. One is a soft lockout when a furnace stops working suddenly but can be restarted again at least twice after the shutdown. When the furnace unit does not restart after three trials, the problem is a hard lockout.

You can face this problem due to three common reasons:

  1. Defective Flame Sensor: If your flame sensor is faulty and needs a replacement, it will not detect the flame resulting in an ignition lockout.
  2. Faulty ignitor: The ignitor doesn’t light the pilot flame when faulty. In this situation, you can try lighting the pilot light using a lighter or matchstick. However, repetitive ignitor failure will lead to an ignition lockout.
  3. Limit switch issues: The limit switch monitors the temperature of the heat exchanger. It also determines fuel pressure. If the temperature is less or more than the required temperature, it will shut down the furnace. A dirty filter also trips the limit switch leading to the ignition lockout problem.

Solution For Furnace Ignition Lockout

  • You should replace the air filter to prevent limit switch tripping.
  • Not only do filters need to be cleaned, but you should also clean the vent pipes. If there is any blockage in PVC vent pipes due to excessive dirt, it will cause a furnace lockout issue. Poorly sloped PVC vent pipes accumulate with debris and other dust particles. You can use a vacuum to clean the vent pipes.
  • Dirty flame sensors also cause this problem. Unscrew the flame sensor and clean it using a scouring pad. Do not rub it using your hands.
  • You should also schedule furnace service twice annually to prevent any such situation.
  • The most common method to solve the ignition lockout problem is resetting the furnace. Read its manual to know which resetting method to troubleshoot your furnace. The best is to contact the manufacturer for this. Furnace resetting depends on the manufacturer.
  • There are multiple ways of resetting the furnace system. If you contact a professional for furnace resetting, you can get it done accurately.


For professional heating, furnace service or fireplace repair in Fairfax, VA, connect with AVS Heating and Air Conditioning. We have been serving in the heating and cooling industries since 1991. We provide services 24/7, all year around. Call us to schedule an appointment without delay!