Furnace High Limit Switch Keeps Tripping

Function of the limit switch.

Furnace high limit switch keeps tripping.

It is a downflow payne 90 have replaced the limit switch. For instance a high limit switch that s supposed to trip at 155f might begin tripping at 130f instead. If the heat exchanger highlighted above gets too hot the furnace shuts down. Once the heat exchanger overheats it trips the high limit switch which shuts the furnace down to protect it.

Rollout switches and high temperature fuses are different from limit switches in that when they open they will not close again unless reset as in the case of the rollout switch or replaced as in the case of the high temperature fuse. When the thermostat calls for heat the furnace burners ignite and begin heating the heat exchanger. One such safety device which also plays a role in the regular heating process is the furnace limit switch. 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.

Some of these parts are shown on the left. This can lead to your furnace going into lockout mode even though it wasn t really overheating. Pulling off the plenum covers i was greeted with a nice airflow the ductwork looks clean and the filter inside has been changed. It s a 160 40f 3 incher that sits near one of the heat exchangers.

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. They will be mounted near where the flame may rollout the front of the furnace due to venting blockages heat. 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.

My furnace is tripping the high limit.