Furnace Limit Switches – What Are They and What Do They Do?

Modern furnaces come equipped with built-in safeguards, one of which is the furnace limit switch, this switch is important to the daily operation of your furnace. You can learn what a furnace limit switch does, how it works, and how you can keep it in good shape.

How Do Furnace Limit Switches Work?

During a heating cycle, your furnace’s burners need some time to heat up. As a result, your air handler needs to wait before switching on, or your rooms will fill with cool air.   You can find the limit switch under the supply plenum of your furnace. It measures the plenum’s temperature and waits until it reaches a comfortable level. When the plenum reaches a certain temperature, the limit switch signals the air handler to start producing warm air for your home.

Reasons Why Your Furnace Limit Switch Stops Working

During the course of time, your furnace’s limit switch can break down due to airflow problems. A dirty furnace filter may cause your heat exchanger to constantly overheat, causing your limit switch to suffer from excessive wear and tear. If your furnace does not have adequate airflow, your limit switch may suffer and may eventually stop working.  If the limit switch fails to transmit a signal to your air handler, it may never turn on during your home’s heating cycle. In addition, if your furnace doesn’t shut off when it should because of a malfunctioning limit switch, it may overheat without shutting down.

What Are the Best Ways to Maintain Your Furnace Limit Switch?

If your furnace limit switch no longer works, you can replace a furnace limit switch yourself. You should test the switch with a multimeter and replace it with a switch that matches the original. Hardware stores sell new switches for up to $20. You can also give us a call or schedule an appointment so we can check it for you.  You can keep your limit switch in working order by having us check your furnace annually. We can inspect your limit switch during your furnace tune-up and see if there are any airflow concerns that may cause the limit switch to fail. It’s also important to change your air filter regularly to ensure that your HVAC system has the proper amount of ventilation.

Furnace Limit Switch Maintenance is Crucial

Be sure that your furnace light switch works properly and that your furnace limit switch is not faulty. You can try to fix a faulty limit switch yourself or have us do it for you. Regularly checking and replacing your furnace’s air filters can also keep you and your family safe.