OEM Lennox Limit Switch — 36W90

The genuine OEM Lennox 36W90 limit switch is a critical safety control that monitors the temperature inside your Lennox furnace's heat exchanger and plenum. If temperatures rise beyond a safe threshold, the switch shuts off the burners to prevent overheating, protecting the heat exchanger and reducing the risk of a fire or cracked exchanger.

A faulty limit switch commonly causes short-cycling, where the furnace repeatedly starts and stops, or a blower that runs continuously. In other cases the furnace may fail to fire at all, or shut down on a limit fault, leaving you without heat. Restricted airflow from a dirty filter or blower issue can also trip a functioning switch — but a worn switch will fail even under normal conditions.

The OEM 36W90 is calibrated to the exact open and close temperatures Lennox specified for your model. A generic switch with a different trip point can allow dangerous overheating or cause nuisance shutdowns. This factory replacement restores proper high-limit protection and guarantees correct fit and calibration for your Lennox furnace.