Are you getting used to hearing the familiar hum of your furnace only to hear it shut off again a few minutes later? Many furnaces can get into the habit of repeating this cycle over and over again. When the furnace turns on then off after a few minutes, you need to figure out the cause so that you can keep your home warm through the blustery winter temperatures.
A furnace that starts and shuts off over and over again is often described as short cycling. There are many potential reasons that your furnace could be short cycling, so let’s take an in-depth look at the causes and their solutions.
Dirty or faulty flame sensor
If your furnace turns off after a few minutes, there is a good chance it is caused by a faulty or dirty flame sensor. This vital component is designed to keep an eye on the gas burner. When it cannot sense that burner, the furnace runs then shuts off and starts again. This could be a relatively easy fix.
Homeowners can enlist the help of a professional to give their furnace a thorough once-over, or they can clean the flame sensor themselves with a lightly abrasive pad. If cleaning it doesn’t correct the problem, the flame sensor may need to be replaced entirely.
Low airflow
When a furnace starts and shuts off, it could be a sign that you have low airflow. The heat exchanger in the furnace will often overheat if there isn’t enough airflow. This particular issue often occurs if the furnace is located in a crowded storage area or has a block in the air inlet leading from the outside into your home. When the exchanger heats up to the maximum temperature, the furnace shuts off after a few minutes.
Remember to replace your air filters!
Solving the issue of low airflow requires a multi-pronged approach. First and foremost, make sure that all of your air filters are clean. These should be replaced every few months to make things easier on your HVAC system and to ensure that you filter clean air into your home.
The furnace won’t be able to pull fresh air into the blower if the air filters are clogged with dust, pet hair, and other debris. You should also make sure to open all of your air supply vents.
Next, you should check the outdoor air inlets to make sure they are not blocked by ice or other debris. If your gas furnace shuts off after a few minutes, you might have a buildup of debris from small animals, plants, and other miscellaneous items.
Faulty pressure switch
A defective pressure switch is another key reason why your furnace turns on then off after a few minutes. The pressure switch should close with airflow from the draft inducer motor through the burner to indicate that ignition is safe.
If the switch is defective, it does not notify the ignition that it is safe to continue. As a result, the ignition is paused after just a few minutes, and the furnace shuts off. A multimeter can help you to determine if there is an issue with the pressure switch.
Faulty draft inducer motor
A faulty draft inducer motor goes hand in hand with a faulty pressure switch. The primary function of a draft inducer motor is to draw air into the burner and out the flue. It also brings in enough air to allow the pressure switch to close and activate the ignition process.
A furnace draft inducer blower
If the draft inducer motor is defective, it won’t provide the proper circumstances for the pressure switch to close and ignite the furnace. This will result in a furnace that turns on then off after a few minutes.
Defective control board
The control board is ultimately responsible for supplying power to all of the inner workings of your furnace. When this piece is defective or broken, the furnace starts and shuts off again rather quickly.
A furnace control board
Without the control board, there will be no power supply to the ignition system that keeps the furnace running for longer periods of time. Unfortunately, there are no simple fixes for a faulty control board. It will simply have to be replaced to correct the issue you are experiencing with your furnace.
Finding the source
If your furnace turns on then off after a few minutes, it could be a relatively minor fix or the sign of a much larger issue. Some handy homeowners are able to solve the problem in an afternoon.
However, you may need more serious professional help. Making major modifications to a gas furnace could be dangerous for you and your family. Be sure to consult with a local professional HVAC company to ensure that your furnace is in prime shape for the coming winter months.
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Kelly
Sunday 12th of December 2021
I have a question. I do not have a local servicing company, and finding it extremely hard to get questions answered. My furnace runtime seems to be short. The furnace heats for 4 mins, the blower kicks in for approximately 1 min. Is that normal? Should I be worried? What could be wrong?
JP
Tuesday 28th of December 2021
@Kelly, did you fine the solution or answer to your question? I have the same issue. I replaced flame sensor and igniter but no luck so far.
Alan Hill
Sunday 1st of November 2020
Is it possible to clean the pressure switch or air inducer ?
Brandy buttgereit
Saturday 4th of December 2021
I have a Coleman Magnum furnace. I threw water on the ground while I was cleaning and the furnace quit turning on with hot air. It sounds like it’s trying to turn on.