One of the great things about modern furnaces is that they have built-in protection against many of the things that can go wrong with your system. One such safety device, which also plays a role in the regular heating process, is the furnace limit switch. Today we’re going to talk about what a furnace limit switch does, what can go wrong with it, and how you can keep it in good shape!

What is a furnace limit switch?

When your furnace begins a heating cycle, it takes a little bit of time for your burners to heat up. As a result, your air handler needs to wait to turn on because otherwise, it would be delivering cool or lukewarm air to your rooms.

A limit switch is a device that’s located under your furnace’s supply plenum. It reads the temperature of the plenum and waits until it gets appropriately warm. Once the plenum reaches a specific temperature, the limit switch sends a signal to the air handler to begin running and delivering warm air to your home.

A limit switch also acts as a safety device for your furnace. If the temperature inside of the plenum gets too hot, it shuts off the gas supply to your burners to prevent your furnace and heat exchanger from overheating.

What happens if your furnace limit switch stops working properly?

Over time, your furnace’s limit switch can develop problems. These problems are most commonly brought on by airflow issues in your system. When your furnace doesn’t have proper airflow, like when it is operating with a dirty filter, your heat exchanger will repeatedly overheat and put your limit switch through excessive wear and tear. This can eventually cause it to malfunction.

Regardless of the source of the problems, a malfunctioning limit switch will result in issues with your system. For example, your air handler might never turn on during your home’s heating cycles because the limit switch isn’t successfully sending it a signal. Or your furnace might overheat without shutting down because your limit switch isn’t shutting off the gas to your burners when it should.

How can you ensure your furnace limit switch remains in good shape?

One way to keep your limit switch in good shape is to schedule a furnace tune-up every year with Jerry Kelly Heating & Air Conditioning. During your tune-up, not only will we inspect your limit switch, but we will also take care of airflow issues with your system that can cause your limit switch to break down.

In addition, it’s important to keep up with your air filter changes. Doing so will help ensure your system has proper airflow, which will prevent the issues we described above.

If you have any questions about a furnace limit switch, or if you’d like a heating system serviced or installed in your home, contact Jerry Kelly Heating & Air Conditioning, your St. Louis furnace installation and repair contractor. We provide service all over the St. Louis area, including towns like Ladue, Lake St. Louis, and Manchester, MO.

company icon