Furnace High Limit Switch Keeps Tripping

One such safety device which also plays a role in the regular heating process is the furnace limit switch.

Furnace high limit switch keeps tripping.

It s a 160 40f 3 incher that sits near one of the heat exchangers. Pulling off the plenum covers i was greeted with a nice airflow the ductwork looks clean and the filter inside has been changed. One of the great things about modern furnaces is that they have built in protections against many of the things that can go wrong with your system. I pulled the blower door off and checked all vents to ensure they are open and it still short cycl.

The limit switch plays an important role in every normal cycle of the furnace. A common reason a furnace short cycles is because the heat exchanger the part that heats your air is getting too hot due to a lack of airflow. Today we re going to talk about what a furnace limit switch does what can go wrong with it and how you can keep it in good shape. This can lead to your furnace going into lockout mode even though it wasn t really overheating.

I found that the hi temp limit switch was tripping the unit. When the thermostat calls for heat the furnace burners ignite and begin heating the heat exchanger. They will be mounted near where the flame may rollout the front of the furnace due to venting blockages heat. Function of the limit switch.

Initially the air above the heat exchanger in the supply plenum is not warm enough to blow into the house so the limit switch keeps the blower off. If the heat exchanger highlighted above gets too hot the furnace shuts down. For instance a high limit switch that s supposed to trip at 155f might begin tripping at 130f instead. My furnace is tripping the high limit.

Some of these parts are shown on the left.