furnace turns on and off frequently

Furnace Turns On And Off Frequently-Investigate 9 Causes

Furnace Turns On and Off Frequently, in other sense we can say Furnace Short Cycling, a silent killer for the Furnace system whereas Furnace plays a prominent role in keeping the house environment warm and comfortable. No doubt it’s an important part of our home.


Wondering, Why does furnace turn on and off frequently? Commonly, the high limit switch shuts the furnace system off because of the Clogged Filter. However, there are some other reasons which might create furnace short cycle issues that cost a ton of money to make the Furnace fully functional.


Most of the people initially may not be able to detect the causes of furnace short cycling. We will investigate 9 root causes of frequent turn on and off of Furnace. Also we will discuss, basics of furnace short cycling, and furnace short cycling repairer cost. Before investigating furnace short cycling causes, we need some initial knowledge, how furnace turns on and off frequently.

short cycling furnace

Any new and full functional furnace turns on and off between 3 to 9 times per hour. And this heating cycle lasts from 7 to 20 minutes. First, the air distributor blower motor sends air to the heat exchanger tube. Burning fuel of a heat exchanger heats the air and then spreads it to the room.


A modern furnace has sufficient safety features that prevent the furnace from doing wrong. Still, it’s a mechanical system. And every mechanical system has shortcomings.


In short cycling, the furnace is turned on and off repeatedly before reaching its intended temperature on the thermostat set point. And the heating cycle lasts from 1 to 2 minutes!


Let’s not make it complicated by pulling technical terms. Here are some reasons discussed below that will help you figure out is its short cycling or not and what to fix to get rid of short cycling.

Reasons-furnace turns on and off frequently

  1. Oversize Furnace: If a newly installed Furnace is short cycling then you might have installed an oversize or stronger furnace than you need. An oversize furnace uses a lot of power to warm your area in very short time that uses tons of power. Many of us cannot realize this reason often. Before checking any other technical details check your Furnace size first. And related that with your home area. Call an expert to measure the proper size of the furnace for your space.
  2. Overheating Of Furnace:  Overheating of a Furnace is a common factor of Short Cycling. One of the primary reasons for overheating is a Blocked Air Filter. Check the Air Filter. If it is needed to clean, then clean it. Fresh and Cool Air cannot pass through the dirty Filter,that heat the Furnace quickly. Most of the Furnace has a high limit switch. When room is heated quickly, then the sensor gets the signal to turn off Furnace and this may cause short cycling.
  3. Faulty Thermostat: Another major reason for short cycling may not because of your furnace at all. Thermostat is also a reason for short cycling. A faulty or malfunctioning thermostat can send wrong signals to the limit switch turn off the Furnace. if you get this then you need to call a professional Furnace repair service as soon as possible.
  4. Wrong Thermostat Placement: Check your thermostat placement carefully.  If the place is hot, then it can send the wrong signal to limit the switch or sensor of the furnace. Few things heat your thermostat, like if there is any big Light bulb nearby, or if direct sunlight hits the thermostat. If the thermostat is too much closed by a warm object or get blocked airflow. Try to move your thermostat and check if the furnace is short cycling or not.
  5. Closed Heat Grill: maybe you may find Air filter is clear, thermostat has the right placement but, your heat Grills are blocked or close by something That you didn’t notice. Check all the heat Exchange Grill. At least 75% of it should be opened. If any furniture or any box or drum is blocking the gate Then remove it.
  6. Exhaust Vent Blockage: This is a dangerous issue because Not only heat but also deadly carbon monoxide cannot pass through A block exhaust vent You might need to check all the way to exhaust vent.
  7. Damaged Heat Exchanger: Don’t forget to check the Heat Exchanger.  Sometimes it could be broken or damaged Because of using it for a long time. Those critical to check but check it regularly.
  8. Air Leaks: Another reason for short cycling Is very simple but unnoticed by most of us. It is poor insulation off your room. Because of the poor insulation system of your room Heath can escape easily and require the furnace to heat up repeatedly. Check your doors and windows Corner if it is not sealed properly is there is any kind of hole in your room by which heat air escaping and creating short cycling of your furnace.
  9. Other Technical Issues: If you have checked all those reasons properly but still you got short cycling then check other technical problems. like your finest system ignition not working properly, or are blower motor is off or not, are there any loose wire connections? check every single reason for short cycling. No possibility can be ruled out.

Furnace short cycling repair cost

Usually, the furnace short cycling repair cost depends on type of furnace, warranty of furnace, service fees, parts replacement cost and labor cost. The national average cost varies from 150 Dollar to 400 Dollar. If the technician finds the short cycling created from minor issues then you can solve the problem even in low price.

In Conclusion

In the end, we can say, furnace is bit complicated system and its problems might be critical sometimes. If you are really concerned about your heating system then you must ensure your furnace system is properly running and will able kick out the furnace turns on and off frequently issue. 


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