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How to Reset Limit Switch on a Furnace: 4 Easy Steps

This article is for informational purposes. Always seek the advice of qualified professionals.

If your furnace limit switch is off, your home won’t heat up correctly. The temperature will not be controlled as needed. And can even present a safety hazard. In that case, resetting the limit switch can help.

How to reset limit switch on a furnace?

Resetting the limit switch on the furnace is quite easy. You’ll first need to locate the switch. It’s probably in your basement. When you find it, uncover it to gain access. From there you can adjust the arms on the limit switch. It’s best to consult the manual before making any adjustments. 

That’s the gist of what you need to do. Keep reading because you’ll need the details I’ll provide.

The Limit Switch – Explained

Your furnace heats up your house. If left running continuously your heating bills will skyrocket. This issue is dealt with by the limit switch.

It controls when the burner starts and stops heating, and when the blower fan turns off. Basically, there are three limits on the limit switch.

An upper limit for when the burner is turned off. A lower limit for the blower to stop. And a third one that ensures the fan turns on once the burner is hot enough. 

Together these switches help the furnace safely maintain the set temperature in the house. 

Resetting the Limit Switch 

The resetting process is quite easy. For your convenience, I will break it up into a few steps. So, just stay tuned with us and learn the way to reset the switch. 

Step 1: Ensuring Your Safety

Before you get to work on the furnace, you’ll have to ensure your own safety. The first thing to do is to turn off the power to the furnace. Locate the breaker labeled furnace and switch it off. 

If it’s a gas furnace, you’ll also need to turn off the gas. Locate the gas supply and turn the valve off. On a completely separate note, you should look into the venting options for your gas furnace.

What sort of venting you use can affect heating performance. 

Step 2: Locating the Switch 

The switch will be at the top of the panel under the heating ducts. To access the switch you’ll have to remove the cover on the panel. Some panels will require screwdrivers to be accessed. 

Step 3: Figuring Out the Switch 

Your furnace limit switch will have three arms. The one on the bottom will be for turning off the burner. If the temperature in the furnace gets too high this switch will turn the burner off. 

The two beside it will be for the fan. One will turn off the fan. The other will turn it on when you find the furnace reaching at a certain temperature.

Step 4: Resetting the Switches

Start by setting the one on the bottom to 200℉. Next, the middle between 100℉ – 110℉ and the last one to 90℉. The middle one tells the furnace to distribute hot air on reaching the set temperature. 

To reset the switches don’t just turn the arms. That can damage the limit switch. Instead, push down on the face of the switch and pull the arms. This will set the pointers to the expected temperature. 

Once you’re done, put everything back in place and trace back your steps. That is, turn on the gas first if it’s a gas furnace. And then turn the power back on. Ideally there should be sufficient separation between gas and electricity

Now, this all seems simple. But what if it can’t be adjusted? Well, in that case, you’ll need to replace your switch. 

Replacing the Limit Switch 

Replacing the limit switch isn’t that difficult either. But first, you should make sure whether you need to replace it or not. If it turns out that you do, then you can go forward to replace it. 

Step 1: Testing the Limit Switch 

You can test the limit switch with a multimeter. Here is a list of some good multimeters:

AstroAI Multimeter Digital MultimeterA battery powered multimeter with a sampling speed of 2 times per second
Crenova Auto-Ranging Digital MultimeterDigital multimeter with sampling speed of 3 times per second

A multimeter is a great investment. And any one of these will serve you well. 

First, take off the covers on the switch and take it out. Then, take out the wires. Next, take out the limit switch. Once it’s out, connect the multimeter to the limit switch. 

If the voltage reading is 0.1 VDC, the switch is fine. Any higher than 0.2 VDC and you’ll have to change it for sure. A reading between 0.1 and 0.2 means that it’s still got some life left.

But you should replace it if the reading is higher than 0.1 just to be safe. 

Step 2: Purchasing a New Switch

The new switch will have to be the same model and make as the existing one. Otherwise, you might not be covered by your warranty if your furnace gets damaged. To match the model, check the label on the existing switch. 

Step 3: Connecting the New Switch

Mount the new switch in the old one’s place. Push it flush against the surface and screw it in. Make sure you do not tighten the screws too much. That might break the device. 

Once it’s screwed in place it’s time to put the wires back in. Reconnect the wires exactly how they were connected before. It won’t be as complicated as wiring a gfci circuit breaker. And there’s a lower possibility for problems as well. 

After that, put the cover back on and screw it in place. Finally, turn on the power to the furnace and let it run. If there are no trips or sudden shutoffs, you are good to go. 

And that concludes my discussion on the topic. 

FAQs

Question: Can a clogged air filter cause the limit switch to trip?

Answer: Yes. A clogged air filter will prevent air from getting in or out of the furnace properly. Thus, it will trap the hot air in and cause the burner to heat up faster. This will cause the limit switch to trip.

Question: How to tell if the fan limit switch is bad? 

Answer: Your furnace fan limit switch might be bad if the blower runs continuously. It is normal for a fan limit switch to deteriorate over time. Usually, a switch should last you 5-10 years without any issue. 

Question: Why is my furnace turning on and off repeatedly?

Answer: The furnace might turn on and off repeatedly, or short cycle, for several reasons. A general reason is a blocked air filter or exhaust pipe. If those aren’t the problems, then the fan limit switches might need resetting.

Conclusion

Now you know how to reset limit switch on a furnace. We’ve covered everything in detail and even provided some extra information. 

You can, however, avoid the hassle of resetting in most cases. All you have to do is keep your air filters clean. I suggest doing it at least once a month. 

There’s no more for us to add to this topic. Keep your furnace functional and stay warm. 

Goodbye!