What is a furnace limit switch?

What You Need to Know About Your Furnace Limit Switch

A furnace limit switch is a small part with a very big and important job. In fact, if this component isn’t working properly, you and your family could be left cold literally – or have other potentially serious issues to deal with. Below, we explore this essential part in greater detail. We also explain why it’s important to contact us about regular furnace maintenance to make sure it’s working as intended.

Furnace Repair Tools - Furnace Limit Switch

What Is a Limit Switch?

Sometimes referred to as a furnace fan limit switch, a limit switch is responsible for triggering the fan to turn on in a forced air furnace. It does so once a certain heat level has been reached within the furnace. If this switch wasn’t there, your furnace wouldn’t respond to the settings for your thermostat, so it’s an incredibly important component, despite it’s small size.

How Does It Work?

Once you turn your heater on, a signal goes from the thermostat to the furnace. After your furnace sufficiently heats up, the limit switch closes. What this does is connect the circuit and get the blowers operating. Once your indoor spaces have reached the desired temperature, the burners turn off and the fan continues to run. It continues to do so until the temperature within the furnace reaches the coolest temperature allowed based on your thermostat settings. Your furnace then cycles on and off or stays off for specific periods of time to maintain the preferred temperature.

The limit switch actually has three main functions and purposes:

  • Turns the blowers on
  • Maintains optimal efficiency for your furnace
  • Prevents your furnace from overheating

How Can You Tell If the Limit Switch Isn’t Working?

Realistically, most homeowners haven’t even heard of this particular furnace part. In all likelihood, you probably won’t even know the limit switch is there and operating when it’s working like it’s supposed to.

If there’s a problem with the furnace limit switch, however, there are two main signs to look out for:

  1. Your furnace fan is running non-stop.
  2. Your furnace fan won’t turn on at all.

Can I Replace This Switch Myself?

Replacing a furnace limit switch by yourself is not something we recommend. Even a seemingly simple type of furnace repair job like this one can be more complicated than anticipated. Plus, it’s important have the right skills and tools to safely and properly locate and remove the defective switch and install a new one. For this reason, it’s best to contact an HVAC professional if you think you have an issue with your limit switch.

Why Reach Out to a Professional HVAC Company?

Winters can get really cold in Illinois, with the coldest month typically being January. In addition to what was mentioned above, this is one of many reasons to reach out to a professional HVAC company about furnace repair involving the limit switch or any other issues that may be affecting your heating system. Routine HVAC and furnace maintenance that includes seasonal inspections can be just as beneficial since smaller problems can be spotted and addressed early.