Why Won’t My Furnace Stay On?

Do-it-yourself furnace troubleshooting can sometimes be very difficult. With hundreds of moving parts and components, your furnace should be a well-oiled machine that effectively heats your Northeastern Pennsylvania home. But, like any piece of equipment, your furnace may experience various problems that may require professional repairs.

Below, we outline a few reasons why your furnace turns on and off intermittently, and why your furnace won’t stay on.

Furnace Troubleshooting

If you find your furnace powering on for a few seconds (or even a few minutes) and then shuts off before its heating duties are done, consider troubleshooting various parts of your heating system below:

Flame Sensor

The flame sensor in your furnace monitors the gas burner. If you furnace shuts off within a few seconds of turning on, your flame sensor may not be detecting a pilot flame, and as a result will turn off the voltage to your gas valve and effectively shutting off your heating system. If your flame sensor is defective, cleaning the sensor may be the only repair necessary, but it will most likely need to be replaced by a certified HVAC professional.

Control Board

The control board within your furnace regulates power supply to various furnace components. You may have a broken control board if your furnace turns on for a few minutes before shutting down again. If this occurs, contact your HVAC contractor to replace the broken control board.

Pressure Switch

Like a defective control board, a broken pressure switch will cause your furnace to shut off after only a few minutes of heating. The pressure switch signals to other moving parts of your furnace that there is the right amount of airflow to function properly. Without it, the pressure switch may cause the ignition process to stall and turn off your furnace.

Limit Switch

The limit switch in your furnace detects the presence of excessive heat in the burner box. If excess heat is detected, the limit switch will shut off your furnace after just a few minutes of operation. The excess heat can be caused by restricted airflow (e.g. a clogged air filter). An HVAC technician can inspect your ductwork and air filters to determine whether the limit switch is defunct, or the problem is being caused somewhere else in your heating system.


Restricted airflow may be the source causing your furnace to turn on and off intermittently. When operating correctly, your furnace should allow the proper amount of airflow through the burner. If your furnace is located in a closet or cramped storage space, there may be insufficient airflow to your furnace, causing it to turn on and off sporadically.

Furnace Repair from T.E. Spall & Son

There’s a reason people call us The Comfort Doctor’s. If you find your furnace turning on and off and will not stay on, give us a call! We’ll send one of our licensed HVAC technicians to quickly diagnose your and repair your furnace, restoring your heating system in no time. Contact us for furnace repair today!

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