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Why won't your HVAC fan turn off?

Make sure your thermostat is functioning properly

Your HVAC fan should turn on and off with the rest of your heating and cooling system. It's normal for the fan to kick on a couple of minutes before heating starts or to stay on for a couple of minutes after cooling stops, but your fan shouldn't run for hours on its own.

This isn't necessarily bad for your fan, but it is usually a sign of a bigger problem. Common causes for fans not turning off when they should include faulty thermostats, bad wiring, and stuck relays. These problems are not easy DIY repairs and should be left to an HVAC professional.

How your fan normally works.

Your blower fan works together with your heating and cooling units, but it's really a separate electrical system. Your furnace and air conditioner simply heat up and cool the air inside of them. Your blower fan is what pulls the uncomfortable air out of your home, sends it through the air conditioner or furnace, and then distributes it back into your home. The thermostat is what tells these separate systems to work together. In normal operation, when your thermostat is set to "auto," it will tell the blower fan plus the heating or cooling components to turn on and off at the same time when the desired temperature is reached. In many systems, the blower fan runs a minute or so before heating or cooling begins and ends to get air flowing. The only other time your blower fan should be running on its own is if you've flipped the thermostat switch to "on" to temporarily run your blower fan for increased air circulation.

Common fan issues.

Why your hvac fan might be running constantly

Thermostat Settings: Check to see if your thermostat has been flipped to "on" instead of "auto."

Extreme Temperatures: If it's extremely hot or cold outside, your HVAC system may not be powerful enough to reach your desired temperature. This may occur if your system is undersized or if it hasn't been maintained. In that case, it will keep running until the outside weather improves.

Faulty Thermostat: If both the fan and either the cooling or heating system are running unexpectedly, you may have a faulty thermostat.

Broken Relay Switch or Short Circuit: If only the fan is running, there may be a broken relay switch preventing the settings you enter on the thermostat from being sent to the fan. Similarly, a short circuit or other wiring problem could be preventing the on/off commands from being sent to your fan.

Fan maintenance.

To prevent future AC and heating issues, it's critical to schedule regular tune-ups with Petro Home Services for your HVAC system. Small problems often build up over time, so you may not even realize you're wasting energy and money each month. Furthermore, once the stress on your system becomes too much, you may find yourself with no heating or cooling at all. This can be especially troublesome if it happens during one of the coldest or hottest times of the year when it's difficult to get an HVAC repair appointment. Along the same lines, if you notice any unusual scraping or whining sounds coming from your HVAC system, you should get them checked out as soon as possible. An early repair is often easier and cheaper than a late repair, which could end up forcing you to replace your entire system.

Consult a professional.

If your furnace or AC fan is constantly running, call an HVAC professional as soon as possible. Trying to fix electrical problems on your own could cause more damage or even create a fire hazard. For a safe and fast repair, contact Petro Home Services. We offer emergency repairs, routine furnace and AC services, and maintenance plans. Call us anytime 24/7/365.

Petro Home Services is proud to not only serve communities in DC, CT, MA, MD, NJ, NY, PA, and RI but we also proudly acknowledge the skills and experience of our expert team behind all resources. With insights on topics ranging from heating oil facts to common air conditioning questions, you can rely on Petro Home Services for facts and information to help you understand more about your heating, cooling and home comfort needs. This article and all articles on the Petro Home Services website have been approved by our team of home service experts.