Why does my furnace turn on and off constantly?

hit furnaceWith a properly working furnace, heat pump, or air conditioner, your home comfort system will cycle on and off as needed to maintain the temperature that is set on your thermostat. It will cycle on when there is a drop in temperature detected, but will also in many cases run a few times an hour, just to help maintain that set point.

However, if your system is cycling on and off more often than you feel it normally should, there could be a potential problem with your unit, or the way it is set up.

Below are some possible causes for a short-cycling system:


Plugged air filter

Did you know that standard furnace air filters should be replaced every 2-3 months? If a filter has not been replaced as often as it should, it can cause major air restrictions in your system, this can cause the unit to overheat, shutting itself off sooner than it normally would. A plugged air filter can eventually lead to much more serious problems than short-cycling, such as a burned out fan motor, or cracked heat exchanger.

Improper function set up on thermostat

When your system is first set up after a unit or thermostat installation, there are internal settings that need to be adjusted in order to suit the type of unit that you have in your home. If you feel that your thermostat may not have been properly set up, ask your service technician to check these settings during your yearly preventative maintenance appointment.

Thermostat placement

Your thermostat should be located in an area that is away from other sources of heat, such as large windows, or other heat producing appliances. A good location for your thermostat is on the main floor, in a hallway.

Furnace safeties wearing out

There could be an actual problem with the furnace itself. As safeties begin to wear out or get dirty on your furnace, it can start to shut the furnace off before the end of its cycle. In most cases, this will eventually lead to a “no heat” issue and it is best to get someone out to look at the unit before this happens. Annual maintenance visits will prevent this from happening.

Improperly sized equipment

If your unit was not sized properly when it was first installed, this could lead to a short cycling unit. Be sure to use a reputable contractor when having your unit replaced.


If you think any of these issues may be happening with your furnace, give us a call to schedule a service call, or maintenance visit. We are always happy to help!