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Does your furnace shut down unexpectedly or run on shorter cycles? If so, you may have a problem with your furnace’s limit switch.
Also known as a high-limit switch, this small (but critical) component helps keep your home safe by automatically shutting off the system when the furnace gets too hot. In this guide, we’ll explain how your furnace’s maximum limit switch works, how it affects your home, and solutions when it fails.
Do you need to fix your limit switch? We can help. Book an appointment with a local HVAC professional.
What is an oven limit switch?
An oven limit switch is a device inside your oven that detects when the internal temperature is too high and turns off the unit as a safety measure. You may also hear it referred to as a fan limit switch or limit switch.
When your furnace is working properly, you don’t have to worry about your furnace’s limit switch. But when it starts to get stuck or malfunction, you may need to learn more about that part and how to fix it.
What does a limit switch do?
Let’s get into a more technical explanation of what your furnace’s limit switch does in the context of your entire heating system. When you raise the temperature of the thermostat, the burners will activate and begin to heat the air inside the room.
When the unit is at the right temperature, a limit switch on the furnace allows the burner to turn on and the furnace will continue to send out heat. If the temperature is too high inside oven, the switch will open, causing the furnace to stop working. The burners will shut off and the fan will continue to run, cooling the oven’s internal components.
When the internal temperature of the furnace decreases, the limit switch will close, allowing the furnace to begin normal operation.
How does the limit switch affect your safety and comfort
Since your furnace uses gas to heat your home, it must have safety features to prevent overheating or breaking. If these safety components fail, necessary parts of the furnace, such as the heat exchanger, can break more easily.
Fortunately, your key acts as a security device to control these variables and keep your family safe. It does this by shutting off power to the gas valve when the furnace exceeds the manufacturer’s temperature limit. If a gas furnace heats your home, install one Carbon monoxide alarm To detect odorless gas in the event of a leak.
What does an oven limit switch look like?
The furnace limit switch has two components. The first is a small button-shaped mounting plate that clips to the outside of the oven chamber. It is attached to a long temperature probe that runs across the oven casing.
Where is the limit switch in the oven?
In most cases, the limit switch will be located inside your furnace hood panel. (You may need a screwdriver to remove this panel, depending on your system model.) However, on older ovens, it may set up on the outside of your oven.
Limit key tripping
Because the limit switch is designed to detect and shut off problems inside your furnace, there are many reasons why it might be tripping. For example, if the furnace continues to shut off shortly after turning on the thermostat, this could indicate problems such as:
- Air flow problems inside the furnace (including dirty air filters), which cause overheating
- Dirty temperature sensor on your oven limit switch
- Defective high limit switch
To avoid these issues, it is important to keep up with the furnace manufacturer’s recommended maintenance schedule. For example, many manufacturers advise changing the furnace filter every three months.
When necessary, you should also clean the temperature sensor in your limit switch to keep it in good working order and prevent tripping. If your switch continues to get stuck after replacing the filter and cleaning the sensor probe, you may have a faulty limit switch (more on that below).
When your switch trips frequently, it may enter a “shut off mode,” in which the furnace will shut off completely. This can only be reversed by having the oven serviced and reset, which should be done by a professional.
How do I know if my limit switch is bad?
As we’ve covered, your limit switch can signal other issues with your furnace that aren’t necessarily related to the switch itself. So how do you know if your switch is the problem? Here are some warning signs.
- Do not turn off the oven blower
- The air coming out of your system is cold
- The system turns on and off frequently (called a “short cycle”)
Schedule an oven repair appointment with a highly rated local technician.
How do you reset the oven limit switch?
If your furnace shuts off several times in a row, it may enter a hard shutdown mode that will require you to reset your switch or the entire furnace system. This happens as a safety mechanism to prevent the furnace from cracking and leaking carbon monoxide into your home.
You may be able to reset the system yourself, depending on the age and model of your furnace. If you have a newer model, you should be able to turn the power off for about 30 seconds and then turn it back on again.
If you can’t reset it yourself or if it turns off frequently, it’s a good idea to contact a professional and have them do a security check. A faulty oven can have life-threatening consequences for your family, so it’s essential to make sure everything is working properly.
Can I replace the oven limit switch myself?
Yes, it is possible to replace the oven limit switch yourself. To do this, you will first need to use a multimeter to test the switch. If it is faulty, you will also need a new key that matches your old one. Here’s how to test the furnace limit switch and replace it if necessary.
- Turn off the electricity and gas from your furnace.
- Locate the limit switch and remove it from your furnace.
- Place the multimeter probes on the switch terminals and check for continuity.
- If there is no continuity, replace the switch with a new model.
Before attempting to complete any work on your own, keep in mind that ovens can be dangerous. Not only does it emit hot air, but it also contains flammable gas and runs on high-voltage electricity. For these reasons, you should not attempt to complete any complex repairs on your fan or furnace limit switch unless you know what you are doing. If not, contact an HVAC professional for assistance.
Don’t want to deal with DIY? Schedule a repair.
Oven reduce repair and replacement costs
If you’re the DIY type, you’ll save quite a bit of money by replacing the furnace limit switch yourself (assuming you already have a multimeter at home). You can find new switches for under $20 at your local hardware store. However, if replacing the switch does not solve your problem, you should contact an HVAC expert.
The cost of a professional oven repair varies depending on the specific problem. In general, you should expect to pay between $100 and $1,000 per furnace repair visit, with an average $270 per repair.
When is an oven repair specialist appointed?
If you’re still having problems with your furnace after replacing the switch, changing the air filter, and cleaning the temperature sensor, it might be time to replace your entire furnace. You can use the HVAC.com Cost Calculator To estimate a replacement price for your oven and contact trusted service providers in your area.
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