OEM Lennox Limit Switch — 87H91

The genuine OEM Lennox 87H91 limit switch is a thermal safety device that guards your Lennox furnace against excessive heat. Positioned to read supply-air or heat-exchanger temperature, it interrupts power to the burners whenever the furnace exceeds its safe operating range, preventing damage to the heat exchanger and surrounding components.

A tripped or defective 87H91 commonly shows up as short-cycling, a burner that lights and then quickly shuts off, no-heat conditions with a high-limit error code, or a blower that won't stop running. Restricted airflow from a clogged filter or blocked ducts frequently triggers the limit, but an aged switch that fails open will also need replacement to restore normal cycling.

Using the OEM Lennox 87H91 ensures the switch matches the exact temperature calibration your furnace was engineered for. Substitute limits with incorrect trip points risk either unsafe overheating or frustrating repeat shutdowns. This direct factory replacement delivers dependable overheat protection and correct operation for your Lennox system.