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What You Need to Know About the Limit Switch

You may or may not be aware of this, but your heating system is actually covered in all manner of switches, valves, and other devices designed as safety measures. There are hundreds of different ways that a heating system could begin malfunctioning, and some of the major ones could end up severely damaging the system or proving dangerous to the home’s occupants. That is why so many safety measures are in place, and why you should know about them. Let’s take a look at one of the most important safety measures: the limit switch.

What is the Limit Switch?

The limit switch is a small part that measures the temperature inside your heating system. Specifically, it measures the temperature of the plenum, the largest chamber of any forced air heater. It is designed to shut down the system in the event that the temperature inside the plenum gets too high. Obviously, an overheating system presents a fire risk, not to mention the damage it can cause to parts that are not designed to withstand that level of heat. As such, the limit switch is one of the most important safety measures in your heating system.

However, there are some interactions between the limit switch and the heater of which you should be aware. Foremost among these is short-cycling.


Short-cycling is what happens when the heating system won’t stop rapidly turning itself on and off throughout the day. When a heater begins to overheat, it activates the limit switch, which shuts the system down to protect it. However, the limit switch doesn’t actually address whatever problem is causing the system to overheat. When the system has cooled off a bit, the thermostat reactivates it, as it hasn’t reached the desired temperature in the home yet. So, the system restarts and overheats again because the issue hasn’t been solved. This leads to an endless cycle of the system overheating and the limit switch shutting it off.

This behavior is extremely harmful to the heating system, putting it under exponentially more strain than it is designed to handle, and increasing the chances of a breakdown. If you notice this behavior, call a professional immediately.

If you’d like to know more, call Comfort Flow Heating to schedule an appointment with us today. We provide professional heating repair services in the Eugene, OR area.

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