Short Cycling: Why does my furnace keep turning on and off?

Short Cycling… Have you heard this term before? Your air conditioner or even furnace can suffer from a short cycling issue, but it is something that can be fixed, and it won’t cost you an arm and a leg.


  • My AC or furnace keeps turning on and off repeatedly
  • My AC or furnace seems to be running more frequently than usual
  • I haven’t changed my temperature in my house, but my AC or furnace is still trying to turn on and off to fulfil a demand I haven’t made


Your system could be short cycling. When a system short cycles, it can kick on and off repeatedly, sometimes multiple times per hour or in extreme circumstances, multiple times per minute. This happens when your system is asked to produce a certain temperature (whether hot or cold), and the requirements have not been met, but your system turns off as if it “thinks” it met the requirement.

Let’s say you set your thermostat at 70 degrees, and it’s currently 65 in your home. Your thermostat will tell your furnace to turn on and produce heat until it gets to the threshold of 70 or above. Your furnace, thermostat, or otherwise may “think” that it has met 70 degrees before it actually has, and another request may occur where the thermostat is telling the furnace, “hotter, please” which causes frequent on and off cycling of the furnace.

Is short cycling harmful?

Yes, short cycling is harmful in many ways.

  1. Your electric bills will skyrocket. Because your system is constantly coming on and turning off, it’s going to be drawing more power without executing the requirements of your heating or cooling demand. Plus, you’ll be using more electricity, oil, gas, or otherwise to keep heating and cooling as necessary.
  2. You will put more strain on your system. You’re asking your system to work one way, but it’s not working the way it should. Constant kicking on and off of the motor, thermostat, and otherwise can make components malfunction or breakdown prematurely.
  3. You won’t be comfortable. Whether you have a noisy system that you don’t want to hear run all night or day, or if your system is never getting to temperature, your comfort will suffer.

What causes short cycling?

An exact determination of what is causing short cycling in your system can be difficult for the typical DIY user. The best way to figure out why your system is short cycling is to call Home Air Plus or a certified HVAC technician. There are a few ways you can try at home to stop short cycling, however.

  1. Check your air filter. A clogged or dirty air filter can cause short cycling. A clogged or dirty air filter can strangle off airflow to your system. Reduced airflow can not only put strain on your system, but it can also cause short cycling symptoms.
  2. Check your thermostat. If you have a very old thermostat, sometimes they can be faulty. It may be time to upgrade to a digital thermostat if you’ve been considering it. If you have a digital thermostat, check your settings and make sure those are set properly. Even a properly set thermostat can be faulty, however, so a replacement may help to take that out of the equation. Even a faulty connection can cause short cycling as well.
  3. Plugged up vent. A vent can be the culprit of short cycling, including improperly installed vents and plugged up ones. Make sure all of your vents, especially your intake vent, are clean and clear.
  4. Other problems that you may want to leave to an HVAC technician: dirty flame rod, water in the tubing, overheating, malfunctioning inducer, circuit board issues, and others.

If you’re suffering from short cycling in your furnace or AC, we can help! With our 24 hour, 7 days a week, 356 days a year service, we can help get your system up to par. Contact us today!

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