Furnace Fan Won’t Turn Off

Has that strange noise of your furnace fan running been perpetuated through the day, and even into the night? Is it failing to shut off, even though the temperature in your house is pristine, or despite all its best efforts are you still uncomfortable? There are many reasons why a furnace fan won't turn off, despite your best efforts; in this article, we’ll go over some common issues you may be dealing with below.

Why is my furnace fan blowing constantly?

If your furnace fan is blowing constantly, it’s worrisome because it can tack on unnecessary costs and greatly inflate your energy bill. It can also cause significant strain on your heating unit, which over time may overheat the system itself and damage individual components. In the grander scheme of things, and in the worst-case scenario, this can necessitate a total replacement of the HVAC unit. 

Why won’t my fan shut off on my furnace?

Furnaces, and the thermostats they respond to, are designed to turn off once the desired temperature has been reached. If this normal process isn’t present, then it may be because of a couple of different issues. Here are some popular reasons why:

Improper Thermostat Settings

If your thermostat is failing to turn off when it needs to, then you’ll want to check your thermostat ASAP. This is often the prime suspect for issues with a fan failing to shut off. See, HVAC systems can sometimes be changed by other members of your household or even bumped when you’re cleaning. It also may be because the system hasn’t been programmed correctly. If your temp is set on the thermostat above what the current temp is, the fan will continue to run until the desired temp is reached.

Improper Fan Settings

If you didn’t already know, a furnace blower motor is designed to work in coordination with the furnace and air conditioner, but some models can work independently. For some homes, the fan may be used to cool or blow air around the home, which helps out if you’re trying to filter indoor air or air out the living spaces once the carpet has been cleaned. It’s a good idea to check your thermostat to ensure that the blower fan unit isn’t set to run continuously. Make sure the settings are set to “AUTO” not “ON.”

Thermostat Issues

Your thermostat is designed to track the existing air temperature inside your home and coordinate with your heating system. If the thermostat is having issues, such as if the wiring is loose, then the entire unit may be malfunctioning. You may need to call a technician to deal with a faulty thermostat.

Dusty Air Filters

Air filters are used in your home to filter dust and dirt while your heat pumps and air handlers are pushing the air around. When your air filters become clogged with dust or dirt, it can cause air movement to become restricted, which in turn may mean your furnace will need to work harder than it has to. You can replace your air filters when they get dirty to mitigate this issue. Some air filters need to be replaced every 1-3 months, whereas some thicker versions may only need a replacement once per every 9-12 months. 

Why is my fan running when my thermostat is off?

If you notice that the blower fan is running, but the air conditioner unit isn’t, it could be an issue with a faulty relay switch. The relay switch could be set to prohibit the settings on the thermostat, cutting its communication with the fan. There could also be wiring issues or a short circuit causing the system to be unable to recognize on and off signals from the thermostat.

Faulty thermostats or relay switches are issues best dealt with by a technician. If you suspect that there is an issue with the relay switch’s communication, call up a reputable HVAC technician. 

How do you fix a furnace fan that keeps running?

There are a few ways that you can personally troubleshoot your furnace fan if it keeps running. If all of these steps aren’t working, don’t hesitate to call a furnace repair technician. Here are some troubleshooting steps:

  • Find the fan limit switch. Your limit switch may be set incorrectly to manual or it could be faulty and needs to be repaired/replaced. 
  • Check to see where the white button is. Make sure that it’s not pressed in. This should be in the lower left corner of your switch. If it’s pressed in, then the switch is set to manual and is making the fan run continuously. It will need to be reset to AUTO if this is the case.
  • If the fan is still running, and the switch is set to AUTO, then it’s time to call a tech because there’s likely an issue that you cannot fix. This could be due to:
    • Bad thermostat wiring, or
    • A limit switch that needs to be replaced due to wear and tear. 

Hiring a professional to deal with your furnace fan is your best course of action. While you can troubleshoot on your own, there’s no guarantee it’ll solve the issue and trying to fix any loose or malfunctioning wiring can pose a danger to you. An HVAC tech is trained in solving issues like these, so let them do what they do best! 

Dunn Heating and Air Conditioning is available 24/7/375 days a year, including after-hours, weekends, and holidays at no extra cost to you! Book your appointment with us today! Furthermore, if your current furnace is deemed unrepairable by one of our technicians and you need a new furnace for your home, make sure to ask us about our discounts and financing options! You’ll also receive a complimentary new system purchase quote from one of our home comfort advisors!