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a red reset button being tested with a voltage meter

Limit Switch

Originally contributed by Jeff Butler • last updated 1/21/2021

These days, many modern household appliances, such as furnaces and hot water heaters, come equipped with safety features, such as limit switches, to prevent serious damage in case they malfunction or break.

Definition

The term limit switch most commonly refers to a device or a sensor that is designed to limit or stop the performance (or over-performance) of an appliance or a machine. When triggered, a limit switch will prevent or limit further operation, typically as a safety measure. Around the home, limit switches are usually found in water heater thermostats or as a furnace high limit switch. Outside of typical household uses, limit switches have many designs and applications.

How To Reset A Hot Water Heater Or Furnace Limit Switch

High limit switches on hot water heaters and furnaces are designed to trip if the temperature gets too hot. Often times, if this happens, the limit switch will need to be reset:

  • Resetting the limit switch on most hot water heaters is fairly easy. Typically, it is a big red button on the upper thermostat of the hot water heater unit. You’ll probably need to access it by removing the plastic cover. Push the button to reset the switch.
  • On most furnaces, the reset button is typically located inside the access panel. Quite often, it is a red button. Hold it down to reset the limit switch.
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