Why Does My Furnace Keep Shutting Off?

One of the most frustrating problems to have with your heating system involves irregular cycling off and on. Called “short cycling” by the HVAC community, this not only causes a lot of noise as the blower turns on and off repeatedly, but it also keeps your heating system from producing heated air to circulate throughout your living spaces.

Short cycling happens when the thermostat tells the blower to turn on in anticipation of the furnace cycling and producing heated air. But when your furnace fails to engage for some reason, it turns off. Since the thermostat still senses the room is too cold, it sends another message to the blower and the cycle starts all over again.

Common Causes of Short Cycling

  • Malfunctioning ignition switch – One of the most common causes of short cycling is a bad ignition switch. This is the switch on newer, high-efficiency heating systems that tells the furnace to turn on and ignite, producing heated air. In this scenario, the switch is getting the right message from the thermostat, but it’s not relaying that message to the furnace.
  • Problem with the pilot light – In older heating systems, short cycling could occur as a result of a problem with the pilot light. The system is designed to shut down for safety reasons if the pilot light fails to stay lit.
  • Faulty thermostat – A third possible reason for your furnace short cycling may not be the fault of your furnace, but rather the thermostat. If the sensor on the thermostat is telling the furnace to turn off prematurely, you could have a short cycling issue.

Diagnosing and Repairing a Short-Cycling Furnace

It generally takes a heating and cooling professional to determine the exact reason your furnace keeps turning off and on. Once your technician gets to the root of your problem, they can replace the malfunctioning part and get your heating system working properly again. The cost of a furnace repair can vary greatly, depending on the source of your short cycling problem. A new thermostat can be purchased for anything between $90 to $400, depending on the model, while a new ignition switch could cost $250 or more plus labor, depending on what type of heating system you have.

To learn more about repairing your furnace in Maryland or Washington, DC, contact Michael Bonsby Heating & Air Conditioning at 301-990-7970. We’ve been helping area homeowners with their HVAC needs for more than 20 years and are happy to put our experience to work for you.

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