OEM Lennox Limit Switch — 84L00

The genuine OEM Lennox 84L00 limit switch is a critical high-temperature safety control installed on the heat exchanger or blower compartment of your Lennox furnace. It continuously monitors plenum temperature and opens the circuit to shut off the gas valve if the furnace overheats — protecting the heat exchanger, wiring, and your home from damage caused by restricted airflow or blower failure.

Common failure symptoms: A faulty 84L00 limit switch commonly causes the furnace to short-cycle on heat, trip out repeatedly, fail to fire the burners, or run the blower continuously. A switch that opens prematurely mimics an overheat condition, while one welded closed removes vital overheat protection — both warrant immediate replacement.

Why OEM matters: Limit switches are calibrated to a specific trip temperature and reset point matched to your furnace's design. The factory 84L00 guarantees the correct temperature rating and mechanical fit, so your furnace's overheat protection functions exactly as engineered. Using a mis-rated aftermarket switch can allow dangerous overheating or cause nuisance shutdowns — and may void your Lennox warranty.