When the temperature drops during the winter season, your family relies on your furnace to keep your home safe and comfortable. Unfortunately, if your furnace suddenly shuts off, cycles on and off repeatedly, or blows cold air, it can be quite frustrating. One commonly overlooked reason behind these issues is the furnace’s high limit switch temperature.
What Is a Furnace Limit Switch?
A furnace limit switch can also be referred to as a high-temperature limit switch. It’s an integrated safety device for your furnace that prevents it from overheating. Whenever the internal temperature of your furnace rises above safe limits, the limit switch will shut the furnace down. This is necessary to protect your system and your home from serious harm.
While this limit switch is great when it’s functioning optimally, it can create a real problem when it’s not. This small but powerful component plays a critical role in maintaining safe and reliable furnace operation. You will find the limit switch monitoring the temperature inside either the supply plenum or the heat exchanger.
How Does a Furnace Limit Switch Work?
All furnace limit switches work in relatively the same way. They continuously monitor the temperature during the operation of your furnace. Inside the limit switch is a temperature-sensitive element, typically made of a bimetal strip or an electronic sensor. As your furnace heats up to a higher temperature than what’s safe, the element reacts and automatically shuts off the burner. Depending on the setup you have, the limit switch may also shut off your blower motor.
After the furnace cools off to a safe temperature, the switch will reset itself. Depending on the furnace you have, this may happen automatically, or you may need to do it manually. Limit switches are specifically designed to protect your furnace from heat damage. They also reduce the safety risk involved with a furnace fire.
One thing to keep in mind about a furnace limit switch is that it typically signals another problem with your unit. Just because the limit switch tripped doesn’t mean the switch itself is bad. Rather, it means it’s doing its job. Many times, issues like dirty air filters, blocked vents, cracked heat exchangers, and failing blower motors can restrict airflow to your furnace.
This can cause heat to build up to dangerous levels. Your limit switch is there to prevent any major damage from happening. However, just like any other component of your furnace, it can malfunction from time to time. It’s always best to have a professional evaluation of your unit when you realize something is wrong, as this ensures an appropriate diagnosis.
Signs Your Furnace Limit Switch Is Failing
As a homeowner, it’s important to pay attention to the functioning of your heating system. This way, you can determine when there’s an issue and respond quickly. You never want to let furnace issues progress, as they can turn into larger problems.
Here are key signs of a limit switch malfunction.
- Short cycling
- Blower constantly running
- Cold air
- Not turning on
- Frequent system shutdowns
- Unusual burning smells
- Error codes on thermostat or control board
Any time that your furnace is turning on or off quickly, it’s considered short cycling. This is the most common indicator of a limit switch problem, as your furnace heats briefly and then shuts down before completing a full cycle. If you notice your blower fan is constantly running even when your furnace is off, the limit switch is likely stuck. When your limit switch shuts your furnace off in the middle of a heating cycle, the blower fan will continue to run, blowing cold air.
If your limit switch is completely faulty, it can prevent your furnace from starting up to begin with. You may get a burning smell coming from your furnace if the limit switch is not shutting it off when it overheats. Shutdowns typically signal an overheating issue, which could be caused by a failing limit switch. Lastly, modern furnaces tend to display diagnostic codes that indicate a limit switch issue for ease of use.
Schedule Furnace Services With Progressive Heating, Air & Plumbing
Progressive Heating, Air, and Plumbing is a trusted HVAC provider for the entire Metro Atlanta, GA area. We’re a full-service HVAC company that can assist with all your heating system repair needs. We repair all different types of furnaces, regardless of their energy source. With our help, you can ensure that your home stays safe and comfortable all winter long.
Contact Progressive Heating, Air, and Plumbing to get furnace high-limit switch temperature assistance today.
