Furnace High Limit Switch Troubleshooting

High limit switch a high limit control switch will turn off the gas to a furnace if the temperature becomes too high. The high temperature limit switch is an important device used in forced air furnaces powered by gas or heating oil. Some furnaces provide extra safety features by wiring two or three high limit switches in a series that check the temperature in the furnace at different points.

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Depending on your furnace model the switch will be surrounded by a silver or white cover.

Furnace high limit switch troubleshooting.

What happens if your furnace limit switch stops working properly. It s also known as a fan limit switch or simply a limit switch. If the high limit switch was bad the furnace should not fire. Over time your furnace s limit switch can develop problems.

A limit switch also acts as a safety device for your furnace. As a safety the high limit. When the high limit switch trips the flame heating element will be shut off and the blower will continue to run to clear the heat. In this episode of repair and replace vance shows how to replace the high limit switch in a gas furnace.

For example if the blower motor stopped running then no air would move through the unit. So to put it simply the limit switch tells the furnace fan when to turn on and when to shut off and it tells the furnace to shut down if it is overheating. Limit switches turn off the burner and turn on the circulating fan if there is a high temperature condition in the furnace. The flames would raise the temperature inside the unit and have no place to go getting hotter and hotter.

As a working example we examine the honeywell combination fan and limit control type l4064b. Locate the white limit switch. It will be located at the top of the panel. If the furnace failure code indicates an open limit or open high temperature switch or open rollout switch it is probable that the furnace has overheated.

The limit switch is a safety switch that monitors t. This article describes in detail the testing and diagnosis of problems with warm air heating furnace combination controls also commonly called the fan limit switch on warm air heating systems. The blower will continue to run until either the system is reset or the limit switch closes. The switch makes sure the furnace is operating safely and at its desired settings.

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. Remove the cover by lifting it upwards or pulling it off to reveal the body of the switch and two metal arms.