OEM Lennox Furnace Limit Switch — 73K20

The genuine OEM Lennox 73K20 is a furnace high-limit safety switch that continuously monitors heat exchanger and plenum temperature to keep your Lennox equipment operating within safe limits. If temperatures rise above the switch's factory-rated setpoint, the 73K20 cuts power to the burners or gas valve to stop the heating cycle, then automatically resets once the furnace cools. It is a key protective control on a wide range of Lennox gas furnaces and air handlers.

Common failure symptoms: When this limit switch fails, you may experience short cycling, complete loss of heat, a blower that won't shut off, or a control board reporting a limit lockout. Repeated thermal stress can cause the contacts to stick or the trip point to drift, leading to unreliable or unsafe operation.

Why OEM matters: The 73K20 is temperature-calibrated for specific Lennox models, and an incorrect trip rating can compromise both comfort and safety. Choosing the OEM 73K20 guarantees the exact calibration, terminal configuration, and mounting your furnace was engineered for — restoring dependable, code-compliant heating performance.