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Furnace Blower Motor Won’t Turn Off? Here’s Why + What To Do

Furnaces of all kinds work on the same basic principle: the blower motor, or fan, takes cool air in and blows hot air out to heat space. The blower motor should only run when the furnace is heating. 

If a furnace blower motor is running continuously even when it is not heating, then there is an issue with the thermostat, the limit switch, the air filter, the ductwork, or the wiring in the thermostat. You can find and fix most of these issues at home without a professional. 

In this article, I’ll show you how to fix the most common blower motor problems yourself and how to identify problems that need a professional repairman, as well as offer tips for how to maintain your heating system to avoid the need for future repairs. 

Simple Do-It-Yourself Fixes

The most common problems with a furnace blower motor are also the fastest and easiest to fix. The thermostat and the air filter are the two parts of your heating system you should look at first.

Thermostat Settings

The first thing to do is to check your thermostat settings and the temperature of the airflow because there are several reasons that your furnace’s blower motor could be running that don’t indicate a problem or serious repair. 

And If the airflow is warm, then the furnace is operating normally, and you should adjust the temperature on your thermostat. If it is set to a temperature that your furnace cannot reasonably achieve (such as setting it to 29°C [85°F] when it is -29°C [-20°F] outside), then your fan isn’t turning off because it is continuously trying to heat your home.

The Limit Switch

If the airflow is cool, check the fan’s setting. If it is set to “on” or “manual,” you need to change it to “auto.” The device that controls the fan when it’s set to “auto” is called the limit switch

When it is working properly, the limit switch will turn the blower motor on and off only when the thermostat settings indicate that the furnace should be heating up. If the thermostat is set correctly, but the blower motor still is not turning off, the limit switch might be broken.

Changing the settings of the limit switch to “auto” is something you can do by yourself, but if the limit switch is broken, a professional should replace it.

The Air Filter

The air filter in your furnace should be cleaned and replaced regularly to keep the furnace functioning. If your air filter is dirty, then the furnace can’t heat properly and will run the blower motor excessively.

As the furnace takes in cool air, it filters out the dust, dirt, pet hair, and anything else that might be floating around the air in your home before pushing the hot air back out. The filter catches these particles.

Over time, these particles build up and restrict or even block the airflow through the furnace. The less air coming through the system, the longer it takes to heat your home, and thus the blower motor will run longer while also being less effective.

Cleaning or replacing your filters regularly will help keep your heating system functioning well, which can help prevent the need for future repairs. You can clean and change your air filter yourself without a repairman, but you should refer to your furnace’s manufacturer to find the right type of filter. 

I recommend the AirX Allergy Pleated Furnace filter from Amazon.com because it filters out common allergens, keeping both you and your furnace healthy.

When To Call a Professional

If you’ve checked your thermostat settings and cleaned your air filters, but the blower motor is still running, then it is time to call in a professional. These repairs are more complex and might require specialized knowledge. 

Wiring Issues

Faulty or aging wiring in any part of your heating system can trigger problems with the furnace’s blower motor. If the wrong wires touch, it can cause short-circuiting. The thermostat and the limit switch are the two places most likely to have issues with the wiring.

Any electrical problems should be addressed by a licensed professional to avoid serious and dangerous damage to your home. 

Thermostat Wires

There are two places in the thermostat where wiring can break down. The first is the wiring within the thermostat itself, and the second is the wiring that connects the thermostat to the rest of the system. 

If the wiring issue is contained to the thermostat, you can replace the unit yourself. I recommend the Honeywell Home 5-2 Day Programmable thermostat from Amazon.com. It has filter-change reminders and can be programmed to adjust the temperature in your home based on your schedule.

If there are problems in the connection to the rest of the system or if there are exposed wires, you should contact a professional as handling electrical problems can be dangerous without proper training.

Wiring issues can occur in thermostats of any age but are more likely to show up in older models. The insulation on the wires can break down over time, exposing the wires and interfering with the circuits. 

While replacing the thermostat itself might solve the issue, a professional electrician or HVAC repairman should handle any replacement wiring, especially if there are exposed or old wires.

Broken Limit Switch

As previously mentioned, a broken limit switch should be replaced or repaired by a professional. Limit switches are complex pieces of machinery that combine mechanical and electrical engineering. Identifying and repairing or replacing them requires training.

The malfunction in the switch could be caused by faulty wiring, which would need to be handled by someone with electrical expertise, but mechanical failures could be repaired by an HVAC repairman. 

Ductwork Issues

You may find that your furnace is blowing out hot air, but your house just isn’t heating up, or the airflow is weak. Both of these issues are caused by leaks in the ductwork.

The air in your heating system moves in one direction through the ducts. There are ducts that take in air (supply) and ducts that push it out (return). Either of these duct types can leak.

If the leak is in the supply ducts, some of the air is leaking out of the system before it reaches the furnace. If the leak is in return, then the hot air coming out of the furnace is escaping into the attic or insulation of your house, rather than being blown into the rooms. Both types of leaks cause the blower motor to run ineffectively and require repairs.

Professionals should find and seal these leaks for you, as it requires specialized tools and sealants. Industrial-grade sealants and adhesives can be dangerous if not handled properly. 

Final Thoughts

Anyone can troubleshoot the most common reasons why a furnace blower motor won’t turn off, no matter what type of furnace you have. The most common problems are quick and easy to solve, whether you fix them yourself or hire a repairman. 

Keeping your air filters clean and monitoring your thermostat settings will help ensure that your heating system is in good repair, which will help prevent more serious problems in the future.