Furnace Won’t Shut Off: Troubleshooting Tips

If you Googled “Why won’t my furnace shut off?” and found this page, you’re in the right place. While your furnace seems to have a mind of its own, don’t panic. There are several things you can do to regain control of your heating system. Here, you’ll learn what to do when your furnace won’t shut off and how to turn off a furnace.

If your furnace is not shutting off, it may take some detective work to determine the reason. Below, we list the five top causes (and the solutions) for why a furnace will not shut off.

Two common thermostat issues can result in your furnace not turning off. Let’s take a look.

Problem 1: Incorrect thermostat settings The most common reason for a furnace fan that won’t shut off or a furnace blowing cold air and won’t shut off is the wrong thermostat settings.

The solution: Check the thermostat settings. The fan setting should be on AUTO. If it’s set to ON, the furnace fan won’t shut off. When the fan is set to AUTO, the furnace fan will only run when the furnace is actively heating the air. Input the desired temperature setting at which you want the furnace to warm your home.

Problem 2: Malfunctioning thermostat Thermostat wiring can come loose or go bad. Thermostats themselves can go bad. If your furnace won’t shut off even when the thermostat is off, the thermostat may be to blame.

The solution: Do some thermostat troubleshooting. Disconnect the wiring or batteries. If the furnace stops, the thermostat is faulty and should be replaced. Consider upgrading to a Trane smart thermostat with professional installation. 

The problem: A dirty or clogged furnace filter prevents proper airflow from reaching your furnace. In normal operation, your furnace blower fan pulls in cold air, and the air is warmed as it passes over the heat exchanger before the blower sends the heated air into your ductwork. 

A dirty filter blocks the airflow. This means your furnace will have to work harder and run longer to get your home to your set temperature. This could be the reason your furnace is running continuously.

The solution: Check your air filter. If it’s dirty, replace it with a new one. Run the furnace as normal. Wait a couple of hours, and if it’s still running nonstop without frigid temperatures, call an HVAC professional.

The problem: The furnace blower fan is powered by a blower motor. This part of your furnace has a limit switch that tells your furnace fan when to start and stop based on signals from your thermostat. If you have a faulty limit switch, your furnace won’t know when to turn off and will run continuously.

The solution: Call for furnace repair. This is not a DIY job.

The problem: Leaky air ducts are letting heated air escape into your attic or walls before it gets forced through the heat registers and into your home. As a result, your furnace will run nearly continuously as it struggles to maintain the set temperature.

Signs of leaky air ducts include:

• Uneven heating and cooling (hot or cold spots)
• Lots of dust
• Higher than normal utility bills

The solution: While not an emergency, you should have an HVAC professional evaluate your ductwork sooner rather than later. Leaky air ducts mean higher energy bills and a less comfortable home. An expert can locate leaks and recommend duct sealing or duct replacement, depending on the severity of the issue.

The problem: Wiring, switches, heating sensors, or even the furnace control board have failed.

The fix: This is not a DIY scenario. You’ll need to call for furnace repair. In the meantime, you can shut the furnace off manually if you don’t need the heat. 

If turning the thermostat to “Off” doesn’t make your furnace stop running, you can turn it off manually. There are two ways to turn a furnace off.

On or near your furnace, there will be something that looks like a light switch. Flip it to the “Off” position, and you cut power to the furnace. This should shut it down.

Find your circuit breaker box - look for a gray or green metal door recessed into the wall in your garage, utility room, or basement. Open the door and look for the breaker marked Furnace. Move it from the On position to the Off position. This will cut power to the furnace and shut it down.

When an HVAC technician arrives for your furnace repair appointment, let them know if you flipped the circuit breaker.

Take care of your furnace if you want it to keep you warm and cozy. Practice regular furnace maintenance to keep your furnace running when you need it. To ensure good airflow, change the furnace filters regularly - every 30-90 days depending on the quality of the air filter and if you have pets. 

Check out our filter maintenance guide for some pointers. 

Just like you take your car or truck in for regular service, you should schedule a yearly furnace tuneup each fall. This can help ensure that your furnace operates safely and efficiently, and runs only when needed.

During the service visit, the HVAC technician should:

• Clean and lubricate the blower motor and other furnace components
• Inspect and tighten electrical connections
• Inspect the gas valve, burners, and ignitor
• Test and calibrate the thermostat
• Test the furnace operation
• Clean the condensate line if applicable
• Make minor repairs or replace worn or failing parts

Many HVAC companies offer yearly HVAC maintenance plans that include fall and spring tune-ups for your heating and cooling systems. You might also be placed on a priority list for HVAC repair, which can be a big deal in a weather emergency.

Help ensure your furnace is always heating your home when you need it. If you have a Trane smart thermostat, opt into Trane Diagnostics for peace of mind. Use the Trane Home App to give your dealer remote monitoring capabilities.  Your Trane smart thermostat sends about your HVAC system in real-time to your dealer, alerting them to any issues, even when you’re on vacation. 

They can run troubleshooting tests to identify the issue(s). In some cases, they can solve the problem remotely. In this situation, you would grant them one-time dealer remote access (DRA). 

If they need to schedule an on-site service call, the technician will arrive with the knowledge gained from remote access. This enables shorter service calls and ensures the technician has the proper replacement parts. 

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by Kimberly Sexton, Senior Systems Engineer

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