OEM Lennox Limit Switch — 80K89

The genuine OEM Lennox 80K89 limit switch is a temperature-sensing safety control that protects your furnace from overheating. Mounted on the heat exchanger or plenum, it monitors supply-air temperature and opens the circuit to shut down the burners if the furnace gets too hot — typically caused by restricted airflow. It also helps coordinate blower operation, and it is a direct-fit replacement built to your Lennox furnace's exact trip temperature.

Symptoms of a bad limit switch include a furnace that short cycles on and off, burners that shut down while the blower keeps running, no heat with a tripped or open switch, or nuisance lockouts even when airflow seems normal. A dirty filter, blocked vents, or a weak blower can also cause the switch to trip legitimately, so airflow should be verified during replacement.

Installing the OEM Lennox 80K89 ensures the correct open and close temperature setpoints your furnace was engineered around. A universal switch with the wrong trip rating can allow dangerous overheating or cause constant nuisance shutdowns. As a safety-critical component, only a genuine OEM limit switch should be used — an inexpensive part that safeguards your furnace and your warranty.