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Why Does My Furnace Keep Running?

A common question we hear from our customers is: “Why won’t my furnace turn off?” The answer depends on exactly which part of your furnace won’t shut off — either the blower (fan) or the burners. These two situations are handled very differently.

While any maintenance or repairs should be conducted by a furnace repair professional, sometimes there are simple solutions you can tackle at home. To help you make the best decision, we’ve put together an easy troubleshooting guide to check before calling a pro.

What to Do When Your Furnace Won’t Turn Off

When the weather is cold, it’s normal for your furnace to be blowing more than usual. However, it should not blow nonstop. Here’s a simple checklist to troubleshoot a furnace fan that’s constantly blowing:

Check Your Thermostat Settings.

  • This first step is the simplest. Most thermostats have three settings: ON, AUTO, and OFF. If your fan is set to ON, the fan will constantly blow. Turn it to AUTO and see if that solves the problem.
  • If that isn’t the issue, try changing your thermostat to the OFF setting. If the fan doesn’t stop when you do this, there could be a malfunction with the thermostat or relay switch. If so, you’ll need to call a professional.

Check the Pilot Light in the Furnace.

  • It’s easy to know if your pilot light is out — air will be coming out of the vents, but it won’t be hot. In this situation, you can try to relight the pilot light yourself. If the light keeps going out or won’t come on at all, it’s best to contact a furnace repair expert.

What to Do When Your Furnace Burners Won’t Turn Off

How can you tell if there’s a problem with the burners? Furnaces are supposed to blow hot air into your home, but there may be a problem if your unit is blowing hot air and won’t stop.

Common causes of this include:

  • Dirty air filters: When an air filter isn’t replaced often (ENERGY STAR® suggests changing it every month), dirt, dust, and allergens can accumulate in your system and worsen the air quality in your home. A dirty air filter also makes it hard for air to pass through it and heat your home. This can cause your furnace to constantly run but never be able to match the temperature on the thermostat, which wears your system out faster. If you suspect this problem, schedule a tune-up to maximize your system’s efficiency.
  • The thermostat is set too high: On a cold Utah night, it can be hard for your furnace to keep up with a high setting on the thermostat. Try turning the thermostat down a few degrees to give your furnace a break. Studies have shown that keeping the home a little cooler at night (between 60 and 68 degrees) is the optimal temperature for a good night’s sleep.

When You Should Call a Professional for Your Furnace

If nothing in the troubleshooting guide above resolves the problem with your furnace’s blower or burners, it’s time to call a professional. In many cases, the issue can easily be remedied with a simple tune-up service, but heating systems are complex and can pose a safety hazard to those without the proper training and skills.

Contact a professional as soon as you suspect a problem with your furnace — waiting can damage your system or cause a costly mid-season breakdown.

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