American Standard Platinum FurnaceIn this post, we discuss reasons your furnace may be shutting on and off frequently. 

What is short cycling?

When a furnace begins to start and stop frequently, this is called short cycling. Persistent short cycling could cause severe damage to the furnace, as well as increase your monthly energy bills.

There can be several possible reasons behind why your furnace performs like this.

Causes of Short Cycling

  • Overheating
  • Dirty or rusted flame sensors
  • Thermostat issue
  • Dirty air filter
  • Blocked air vents
  • Oversized furnace


One reason that your heater must be turning down because of overheating of the heat exchanger.

The reason the furnace shuts down is to protect it from cracking as the exchanger overheats. As the exchanger cools down the furnace cycle turns on.

Dirty flame sensors

A dirty or rusted flame sensor can prevent the furnace from heating correctly because it can’t confirm the presence of a flame.

The flame sensor is used to confirm that the gas valve is open, and the flame exists in the furnace. If the flame is not in the furnace, the sensor closes the gas valve and in order to prevent dangerous levels of gas from collecting.

If the flame sensor gets coated in dirt or rust, it may become unable to register the flame. It will then shut off the gas valve. This causes the furnace to turn on again and again but then shut down quickly because of the flame sensor.

In these cases, a professional will need to clean the flame sensor.

Thermostat Issues

The main job of the thermostat is to tell your furnace when to turn off and on. An issue with the thermostat could be the reason for short cycling, rather than the furnace.

There could be a technical malfunction with the thermostat. It could also be improper placement of the thermostat. This could include placing the thermostat near a heat source such as vent or sunlight from a window which fools the thermostat sensor into thinking that your house is warm and turns off the furnace. Make sure that the thermostat is placed on an interior wall away from heat sources.

Related Post: Types of Thermostats

Dirty Air Filter

A dirty air filter can cause overheating.

A clogged filter blocks air over the heat exchanger, meaning that it retains too much heat. The solution for this can be checking the filters once a month or as needed according to the instructions on your filter (1-3 months)

Blocked Air Vent

Shutting supply vents, or blocking vents with furniture and drapes can cause the heat exchanger to overheat.

If you close the vents, this increases pressure in the air ducts, which causes the blower to blow less air because it’s designed to push up against a certain amount of pressure. This low airflow means the heat exchanger exchanges less heat and causes too much heat builds up.

Oversized furnace

Overpowered furnaces heat smaller homes quickly but unequally. This results in short cycling in order to maintain consistent temperatures throughout your home.


If you have doubt about any of these issues, make an appointment with an expert and get it checked.

A Climate Services & Systems Inc.

Do you need help getting your furnace working again?

Contact us online or phone 630-393-9500

We serve Warrenville, Carol Stream, Downers Grove, Geneva, Lombard, West Chicago, Naperville, and Batavia and nearby communities.


Picture source – Safe bee