Why won't my furnace stop running?

Author: Angie Brown  |  Last update: Thursday, August 7, 2025

The short answer is your furnace won't turn off due to some kind of error or malfunction within your furnace, thermostat, or HVAC system. It could be the wrong thermostat setting is being used, a clogged air filter or your thermostat itself is no longer working properly.

What to do if your furnace won't shut off?

If your gas furnace won't turn off, it could be due to a faulty thermostat or a problem with the furnace's limit switch. Start by checking the thermostat settings and making sure it's not set too high. If that doesn't work, try turning off the furnace at the breaker and then back on again.

How do you fix a furnace that keeps running?

When a furnace runs constantly, it probably means that something is dirty or clogged. The filter is the first thing you want to check, especially if you do not replace your filter as often as recommended (once a month during the heating season).

What would cause a furnace not to kick off?

The cause of your furnace not blowing hot air could be the thermostat configuration, a dirty air filter, the high limit switch, a clogged condensate line, insufficient fuel, leaky ducts, ignition problems, a blocked burner, flame sensor issues, gas valve malfunctions, a cracked heat exchanger, or a clogged coil.

What makes a furnace run continuously?

Clogged Air Filter

A clogged filter will result in very little cold air being drawn into the furnace and much less hot air blowing out of your vents. This will cause your unit to run for much longer since it isn't producing nearly as much heat.

FURNACE won't shut off! Top reasons why your furnace keeps running

Is it bad for a furnace to run nonstop?

Running your furnace constantly can put extra strain on the system, potentially shortening its lifespan. It is important to have your furnace regularly maintained to ensure it is in good working condition and not being damaged by constant use.

Why does my furnace keep running even when the thermostat is off?

Incorrect settings on your thermostat or fan limit switch can cause the fan to run continuously. Faulty wiring or a broken fan limit switch can also cause your fan to keep running. You can diagnose and fix some furnace fan issues on your own. Faulty wiring or a broken switch will require professional repair.

What to do if heating won't turn off?

Check the Thermostat

Your thermostat controls your furnace and basically tells the unit when to turn on and off. It's often to blame when your furnace won't stop running. Sometimes having the heat turn off is as easy as adjusting an incorrect thermostat setting. Make Sure Your Thermostat is Set to “Auto”.

How to tell if a thermostat is bad?

A bad thermostat can be detected when your AC or furnace is not turning on, your HVAC systems are not turning off, the thermostat not responding, your HVAC system is short-cycling, the room temperature not matching the temperature displayed on the thermostat, and the programmed setting resetting themselves.

Why does my heat keep running after it has reached the set temperature?

A dirty air filter can get clogged and reduce air flow through your home's heating system. This means the air your furnace is heating isn't reaching your living spaces and causing your furnace to cycle on more often and work longer while it's on.

Why is my furnace blower not shutting off?

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.

What would cause a blower motor to continuously run?

A Bad Circuit Board or Shorted Wire. The circuit board or wiring in your furnace may be faulty, causing the fan to run continuously. This is a complicated problem that requires professional furnace repair.

How long should a furnace stay running?

Furnaces typically run for about 10 to 15 minutes in moderate weather. Extreme cold can result in longer cycle times.

Can I just turn my furnace off?

Ultimately, there are very few situations where shutting off your system will lead to lower utility bills or savings. That's because adversities and potential damage usually arise when you power off your furnace. During winter, it's especially risky to keep your furnace off for any period.

Can a bad thermostat cause a furnace to shut off?

Faulty thermostat.

Old wiring or dead batteries: Replace batteries or old wiring to ensure accurate temperature readings. Thermostat location: If your thermostat is too close to a heat source (like sunlight or a heat register), it can misread the temperature and cause your furnace to keep shutting off.

Why is my heating staying on when it's turned off?

Why are my radiators not turning off? To conclude, if your radiators are not turning off when the heating is off there is likely a problem with the diverter, check, or solenoid valve. If these valves get stuck they will keep sending hot water to the radiators even when the heating thermostat is off.

How to reset a thermostat?

Most modern thermostats will have a clearly marked reset button inside the panel. It's usually small and recessed, so you might need a pointed object like a paperclip to press it. For those wondering specifically how to reset air conditioner thermostat models, the process is generally the same.

Why does my furnace keep kicking on and off?

A furnace cycling on and off repeatedly can be caused by various reasons, from dirty filters and obstructions in ducts and registers to incorrect thermostat settings and faulty limit switches. By following the steps above, you can help prevent your furnace from cycling too frequently and save energy costs.

How do I know if I need a new thermostat?

If your thermostat has fresh batteries but suddenly lacks power, flashes, or isn't responsive to adjustments, it may need replacement. If resetting the thermostat doesn't resolve the problem, you may have wiring problems or faulty components causing your thermostat to not turn on.

What happens when your furnace won't shut off?

Here's Why Your Furnace Won't Turn Off. The short answer is your furnace won't turn off due to some kind of error or malfunction within your furnace, thermostat, or HVAC system. It could be the wrong thermostat setting is being used, a clogged air filter or your thermostat itself is no longer working properly.

What do you do when your heat won't stop running?

If your heater won't turn off, the first thing you do is check the thermostat. The thermostat controls how the heating system runs. It detects the indoor temperature and signals the furnace to start or stop. So, if the thermostat malfunctions, it can signal the unit to run continuously.

Why is my central heating constantly running?

Several internal boiler issues can cause continuous operation. These include insufficient system pressure, burner blockages, and frozen condensate pipes during cold weather.

Why is my furnace running nonstop?

The most common reason why a furnace run continuously is because of a dirty furnace filter. Dirty air filters restrict airflow and force your unit to work harder to heat your house. Be sure to check your air filter every month and replace it when necessary.

How much does it cost to replace a thermostat?

The average cost of a new thermostat, including installation, ranges in price from $50 to $500 or more based on several factors including the type of thermostat, labor costs, the complexity of the installation, and more.

Why wont my furnace blower shut off?

If your furnace fan won't turn off, you most likely have one of these 3 problems: Your furnace fan limit switch is set to “manual override” The fan limit switch is faulty and needs to be replaced. There's a problem in your thermostat wiring.

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