OEM Lennox Limit Switch — 73W20

The genuine OEM Lennox 73W20 Limit Switch is a critical high-temperature safety control that monitors the heat exchanger and plenum temperature in your Lennox furnace. It signals the blower to run and, most importantly, shuts off the gas valve if temperatures climb beyond safe limits — protecting your furnace and home from overheating and heat exchanger damage. It is calibrated to the exact trip and reset temperatures your model requires.

Common failure symptoms: A faulty limit switch often causes the furnace to short cycle, shut down mid-heating on a limit trip, run the blower constantly, or fail to fire at all. Overheating from restricted airflow, a dirty filter, or a bad blower will fatigue the switch, and the bimetal element can weaken or stick over time.

Why OEM matters: The OEM Lennox 73W20 switch is set to the precise temperature thresholds your furnace was certified with. A generic switch with the wrong trip point can nuisance-trip or, worse, fail to open when it should — a genuine safety hazard. Installing the factory-specified limit switch restores accurate overheat protection and safe, reliable furnace operation.