Heater On and Off? Find Out Why.

You’re relaxing in your living room binge watching your favorite show when the furnace clicks on. After just a few seconds, it turns off again. This process repeats itself several times an hour.

Is this just normal furnace behavior? Is it okay to ignore it and keep watching your show? Or should you turn off the tube and call for help?

A properly sized furnace should come on and off about 3 to 8 times per hour. Keep in mind, however, that the exact number of on-off cycles for your furnace might vary based on a number of factors:

  • The size of your house
  • Whether your furnace is the right size for your house
  • The outside temperature
  • Whether you have the right amount of insulation

Short Cycling: When Your Furnace Turns on Then Shuts Off

A properly functioning furnace should stay on for at least several minutes before turning off again.

If your furnace comes on then shuts off after just a few seconds to one minute, and it does so repeatedly, that is called short cycling and it is not considered normal. It typically occurs as a safety precaution against overheating.

Why is short cycling a bad thing? There are two main reasons:

  • It can cause your furnace to break down. Repeatedly turning on and off in rapid succession, instead of staying on for several minutes, puts a strain on your furnace and can lead to expensive repair or replacement costs.
  • It can increase your energy bills. It would be absurd to try to drive your car while turning the ignition on and off. Short cycling means the furnace is running inefficiently, which wastes energy and increases your utility bills if left unrepaired.

What Causes Short Cycling?

Short cycling usually occurs when the furnace is either too hot and/or getting poor ventilation.

  • Furnace is too hot. Your furnace comes with a high limit switch that will automatically turn off when the temperature reaches unsafe levels.
  • Poor ventilation. Another safety feature is the flue limit switch. This turns the furnace off when air isn’t properly ventilating out of the exhaust flue.

There are a few things that can cause these problems and lead to short cycling:

  • Dirty air filter. A clogged filter restricts air from getting to your furnace and is the most common cause of short cycling. Without air blowing freely over the heat exchanger, your furnace will overheat and shut down.
  • Thermostat issues. If your thermostat is malfunctioning, or if it is positioned too near a heat source, it will misread the temperature and cause short cycling.
  • Furnace too big. Your furnace must be properly matched to the size of your home or business. If it is either too big or too small, it will not work as efficiently.

What to Do When Your Furnace Turns Off and On Repeatedly

If your furnace keeps going on and off, investigate the following things before taking further action:

  • #1: Check your air filters. You should change your filters at least every 3 months, and even more if they get clogged.
  • #2: Check your thermostat. First turn it off, then open it up to see if the wires are connected and working properly.
  • #3: Check furnace motor. Is the air coming out of your vents? If not, have a technician come out and inspect your furnace.
  • #4: Check the exhaust flue on the roof of your house. Is there gas coming out of the flue? If not, have it checked for blockage.

Is your furnace cycling on and off too frequently? Contact us at Complete Electrical Solutions.

Our certified electricians can diagnose the problem, answer your questions, and help you get your system working properly again.

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