Gas Furnace Limit Switch Not Working

Limit switch set wrong.

Gas furnace limit switch not working. A high limit control switch will turn off the gas to a furnace if the temperature becomes too high. The gas fired forced air furnace fan limit switch in the photo below is pointed to by the red arrow. How to test and replace the fan limit switch on a furnace things to check before replacing the limit switch. For example if the blower motor stopped running then no air would move through the unit.

Over time your furnace s limit switch can develop problems. The flames would raise the temperature inside the unit and have no place to go getting hotter and hotter. Belts sticking worn or damaged. Furnace not working no gas flame.

The oil fired furnace fan limit switch shown in our photo below is in use on an oil fired warm air furnace where we can see about 3 4 of the silver colored dial where the fan limit switch settings are made red arrow. Typically the lower pointer should be set to about 90. Limit control needs adjustment. It s possible to reset the switch at home when necessary by following a few simple steps.

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. According to honeywell voltage transients or even other conditions around the limit switch that impact the temperatures to which it is exposed can affect the cut on or cut off temperature behaviors of the switch but the company s instructions to not mention apparently excessive on off cycling of the furnace blower fan traced to the limit. A limit switch also acts as a safety device for your furnace. What happens if your furnace limit switch stops working properly.

If the blower came on at the same time as the burner it would pump cold air through the house at first. The function of your furnace limit switch is to tell the fan when to turn off and on depending on the temperature in the home. Spray squeaking drive belts with belt dressing. To troubleshoot a misbehaving gas furnace start with the easiest explanations and solutions then work your way to the most complicated.

The limit switch includes a sensor in the heat exchanger to. If it is set to off or auto the furnace s limit switch must be adjusted. Replace worn or damaged belts. Mount and fasten access panels correctly.

If your gas furnace is blowing cold air a number of factors could be to blame many of which you can address on your own without the immediate help of a service professional. Also a malfunctioning switch may not send signals to the air handler successfully which may cause the handler to never turn on. Call a furnace repair technician to adjust the limit switch or follow the instructions in your owner s manual to reset the pointers on the fan side of the limit control.