Furnace Ignition Lockout: Causes & Solutions

What does ignition lockout fault mean? Is your furnace continually shutting down? Is your furnace not responding to any attempts to turn it back on? Your furnace could be experiencing an ignition lockout, which must be reset.

Modern furnaces have a variety of safety sensors that ensure the unit’s proper operation. The furnace shuts off if any sensors detect unsafe conditions. This prevents safety hazards and damage to the unit. The furnace will remain in this condition until the Murrieta heating repair technician can manually reset it.

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What does an ignition lockout fault refer to?

The furnace controller will turn off power and fuel when it detects that there is an unsafe condition. This condition is called an ignition lockout and can be caused by many sensors in your furnace. If your furnace is locked out, it will most likely remain in that state until it’s reset. Many homeowners leave their furnace locked out after they try to restart it several times. The sensor may have detected an unsafe condition.

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What causes furnace ignition locking out?

The majority of furnaces that go into ignition lockout are caused by problems with flame sensors, igniters or limit switches. Here are some of the most common causes of lockouts.

Defective flame sensor

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Defective flame sensors are one of the most common causes of lockouts. When the furnace turns on, the sensor will check for fire. If the sensor is faulty or dirty, it won’t be able to detect the flame and the controller will stop the ignition sequence. Modern furnaces allow you to start the furnace twice more before it locks out.

Faulty igniter

The igniter is another frequently encountered lockout culprit. If your furnace igniter does not activate within a couple of seconds, the flame sensor won’t detect the flame, and the controller will stop the furnace from starting. Your furnace will likely lock out after the third attempt. The pilot light on your gas furnace may cause the lockout.

Limit switch response

Your furnace also has a limit switch that monitors heat exchanger temperatures and fuel pressure. If the temperature or pressure are too high, the limit switch will trip, causing the furnace’s to turn off and go into lockout mode. Altering the air flow may cause the limit switch’s trip by dirty filters. Modern furnaces may have status codes lights that can help you determine what caused the lockout.

What is the difference in a hard lockout and a soft lockout?

There are two main types furnace lockouts to know: a hard lockout and a soft lockout. As we’ve already explained, your furnace controller will stop the ignition sequence and prevent unsafe operation if the sensor doesn’t detect the flame within a set time period. This semi-shutdown is known as a soft lockout, and you will be able to attempt to start the furnace again, usually two more times.

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A hard lockout happens after several repeated soft lockouts. Most furnaces require three attempts to turn on the furnace before it locks itself into hard mode. You will need to reset the unit manually if this happens. This can be done by calling your HVAC technicians.

How can you fix an ignition lockout on your furnace?

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The specific procedure to get your furnace out will vary depending on who is responsible. Here’s what you can do before resetting your furnace:

  • Clean or replace the flame sensor: Inspect the furnace flame sensor to look for cracks and signs of damage. If you see only soot, or some corrosion, please refer to our guide on cleaning flame sensor. If that doesn’t fix the problem, replace the sensor and try again after you restore the furnace from lockout.
  • Clean or replace the air filter: A clogged air filter can prevent adequate air supply to the system, tripping the limit switch. You can simply replace the filter and check if the problem has been solved. You should replace furnace filters as often as possible to protect your family’s safety.
  • Inspect and clean the vent pipes: Look for debris and signs of obstruction inside your vent pipes and clear any blockage you find. If you’re unable to remove the blockage yourself, it is best to call HVAC professionals to repair the damaged section.

Resetting the furnace

Regardless of the culprit, you will have to perform a reset procedure to get your furnace out of lockout. Modern gas furnaces can usually be reset by turning off all power, waiting approximately 20 seconds, and then switching back on. Some furnace models will go into lockout and then try to power back on after 1-2 hours. If your furnace has a pilot light, you may need to relight it following the manufacturer’s instructions.

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If none of the suggestions work, you can contact a skilled HVAC technician to have your furnace inspected and repaired.

Contact San Diego’s favorite heating repair company in Murrieta

What causes furnace ignition lockout? After being named the favorite HVAC company in San Diego in the 2020 Union-Tribune Poll, we can proudly say that you won’t find better heating and cooling professionals in the area. Action Air Conditioning, Heating & Solar is a long-standing HVAC company offering top-quality service to homeowners across Riverside County and San Diego County. Whether you need help with your furnace or air conditioner, don’t hesitate to give us a call. Get in touch with us today!

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