Furnace Limit Switches: 5 FAQs

What’s a furnace limit switch? Maybe your HVAC technician has told you that something is wrong with your furnace limit switch. Or maybe you’ve been searching online about your furnace’s problems and have come across some mention of this critical part of the furnace. Here’s what you need to know about furnace limit switches.

1. The Furnace Limit Switch is Essential

The furnace limit switch is the switch in the furnace that turns the furnace blower fans on and off. The furnace blower fans are what take the hot air your furnace generates and sends it through your air ducts and into your home. When the furnace limit switch isn’t working, all kinds of problems can crop up, but often your home will feel cold.

2. The Switch’s Limits are Temperature Based

There are three main tasks the limit switch has: blow hot air into the home, avoid blowing cold air into the home, and preventing overheating that could damage the furnace’s heat exchanger. Each task is triggered by temperature. The exact temperature will depend on your model, but it could look something like this:

• Below 60 degrees Fahrenheit: The switch will turn off, to prevent blowing cool air into the home, or you could be uncomfortable. Imagine feeling a breeze in your home in early fall and you’ll see what this is preventing.
• Above 70 degrees Fahrenheit: The switch will turn the fans on, to blow the heat the furnace is generating into the home. This is normal operation.
• Above 150 degrees Fahrenheit: The switch will stop the burner from operating in order to prevent the furnace from overheating or becoming a safety risk. Typically, if the switch is triggered for this reason, something is wrong with the furnace.

Are you looking for home heating options? Contact our team at Tempasure Heating & Air Conditioning today.

3. It is also Called the High Limit Switch

If you look online and find information about the high limit switch, that is the same as the furnace limit switch that we’re talking about here.

4. Certain Problems Can Trip it Early

If your furnace keeps turning off then it is likely that you have some kind of issue that is causing the switch to either trip due to temperature, or trip earlier than it should. Potential problems include:

• Damage or age has broken the high limit switch.
• The temperature sensor is damaged or dirty, so it can’t read the temperature properly.
• Airflow in your furnace has been impacted to the point it is overheating. This may be due to a broken fan, a full filter, a clog, or another issue.

5. There are Signs Your Switch has Broken

If you have the following signs, your switch might be broken:

• Your furnace blowers run continuously
• Your ducts are blowing cold air (and the air conditioner is not on)
• The system turns on but then off very quickly

Are you looking for more information on furnace limit switches? Contact Tempasure Heating & Air Conditioning today. We would be happy to answer any of your questions.