Furnace Not Turning Off? 7 Common Causes to Check

Stuck trying to figure out why your furnace won’t turn off?

Unfortunately, I’ve been there too. I know how annoying it can be to have this happen. After all, furnaces should make our lives easier, not the opposite.

But, don’t worry. You’ve come to the right place to fix this problem.

If your furnace won’t turn off, there’s a good chance the thermostat is set to “ON” or its settings have been changed. This may also happen due to a dusty air filter, an open gas valve, or an electrical issue.

Keep reading to learn how to fix these problems and turn off your furnace!

Solving A Furnace That Won’t Turn Off

We all like to feel the comforting warmth of the furnace during the cold months. But what if the heat coming from your furnace is no longer comforting, but is actually rather stifling, or even sweltering? And if that wasn’t bad enough, what if you can’t seem to turn the thing off?!

Don’t worry, though. In this article, you’ll learn the 7 reasons why your furnace won’t turn off. You’ll also learn how to fix the problem on your own!

#1 The Thermostat Is Set to “ON”

If your furnace won’t turn off, there’s a good chance the thermostat is set to “ON”.

When this happens, blowers continue to operate and circulate air around the room (even with the heating system off).

Luckily, this issue can be easily solved by changing the thermostat from “ON” to “AUTO”. This way, your furnace will only run during a heat cycle.

#2 The Thermostat Settings Need Changing

If your home is anything like mine, every day is full of action. The kids are running around, your pets are bouncing about. There’s never a dull moment.

With all of that happening, it would be so easy for the thermostat to get knocked, and its settings accidentally changed. 

Take a look at your thermostat’s temperature settings. If it is set too high, the thermostat will keep running even if it feels like it is already too warm inside. 

What’s the best thing to do? Turn the thermostat back to a good household temperature. (And if necessary, put a little tape over the dial or set up a mini barricade around the thermostat, so it isn’t troubled again).

With the thermostat set correctly, the furnace should turn off when your home is warm enough.

#3 The Air Filter Is Dusty

Now, I know what you’re thinking. There are already enough things around the house to dust and keep clean, and you now have to worry about a dirty air filter too! But this one is easy, promise. 

If your furnace won’t turn off, there’s a good chance dust and dirt are clogging the air filter.

This happens because of the reduced air movement when the filters are dirty, which forces the furnace to work harder and longer than it needs to. 

So, how can you stop your furnace from doing overtime? Try the following:

1. Open the air filter’s access panel
2. If the filter is dirty, remove it and replace it. You should replace your furnace’s filter at least once a year. But you might need to replace it more frequently, depending on the air quality where you live and how often you use the furnace.

#4 Reset Your Furnace

If you’ve tried the three fixes above, but your furnace won’t turn off, you might need to reset it.

I know, doing this may sound like a simple solution, but believe me, thousands of people have found this tip helpful.

If you’re not sure how to reset your furnace, do the following:

1. Set the thermostat from “ON” to “AUTO”
2. Gently turn the furnace off at the switch or the plug
3. Leave the furnace off for 30 seconds. The furnace should come to a complete stop.
4. Turn it back on. The furnace should have reset itself and should not turn itself back on.

#5 The Relay Is Stuck

Now here comes one of my favorite fixes. Is your furnace making you feel frustrated and in need of letting off some steam? Then make sure you complete this step. 

If your furnace won’t turn off, it could mean that an element is stuck.

To solve this issue, you’ll need to cause a vibration to see if we can shift any stuck components, such as a mechanical switch or a relay on a circuit board. Here’s how to do it:

1. Turn the furnace on
2. Put the palms of your hands on the furnace and give it a jolt with your hands, or smack it. This should make the blower stop. 

If jolting the furnace fixed the problem, then it’s likely that whatever component was stuck will get stuck again.

Giving the system a jolt is a good temporary fix. But to solve the problem long-term, you will need an HVAC specialist to repair the system.

#6 The Gas Valve Is Stuck Open

What if you unplug your furnace or turn it off at the switch, and it still keeps running? This is an unusual issue but by far impossible. 

If your furnace won’t turn off even when you have switched everything off, the gas valve could be stuck open.

If the valve is mechanically stuck, it will continue to burn natural gas even when the furnace is off. 

What should you do in this case? Take a look at the following instructions:

1. Locate the gas stop. It should be near the furnace. 
2. Turn the gas off
3. Contact your HVAC specialist to see why your gas will not turn off automatically

#7 The Contacts of the Relay Are Pitted

What if you have tried all the fixes so far in this article, but still cannot get your furnace to shut off? Then you might have a problem with some of the contacts in the relay.

If there was a little spark inside the system, the contacts could be pitted and arc welded themselves closed. This kind of malfunction will stop the contacts from opening and could explain why your furnace won’t turn off.

So, what should you do to fix this issue?

Now, this is an electrical issue that I do not recommend you tackle yourself. The best thing to do is to call an electrician or your HVAC specialist to have a look at it. 

The electrician will also check the system for a possible short circuit that could also be the cause of the problem.