How to Locate the Limit Switch on a Gas Furnace

With an annual fuel utilization efficiency (AFUE) rating of 90 percent or greater, gas furnaces are a popular and efficient way to heat your home during chilly weather. Residential gas furnaces contain an internal component, known as a limit switch, that shuts down the furnace when the gas burner assembly overheats. If your gas furnace shuts down due to overheating, you'll need to locate the limit switch to reset your appliance. Locating a limit switch in a gas furnace is so simple that it takes just minutes.

Step 1

Disconnect the electricity to your gas furnace before attempting to locate its limit switch. Open your circuit breaker box and identify the switch that controls the electricity to your furnace; flip the switch into the "Off" position to eliminate the risk of electrical injury.

Step 2

Locate the furnace's control access panel; this is the top-front panel on upflow models and the bottom front panel on downflow models. Grasp the sides of the panel and lift it straight up while simultaneously pulling it toward you to remove it from the furnace. Set the removed panel aside or lean it against the furnace.

Step 3

Locate the gas burner assembly in the furnace control cabinet; look for a series of cylinders behind a curved pipe (the gas manifold). Look for a raised red button just above and to the left of the gas burner assembly; this is the manual reset limit switch.