OEM Lennox High Limit Switch — 26G78

The genuine OEM Lennox 26G78 high limit switch is a temperature-sensitive safety control that monitors the heat exchanger and plenum temperature in your Lennox furnace. If the airflow is restricted or the unit overheats, the 26G78 opens the circuit and shuts down the burners, preventing damage to the heat exchanger and reducing fire risk. It automatically resets once the temperature returns to a safe range.

Common failure symptoms: A failing high limit switch often causes short cycling (the furnace repeatedly firing and shutting off), no heat, or the blower running continuously. A switch that stays open indicates it has tripped or gone bad, while a stuck-closed switch defeats critical overheat protection.

Why OEM matters: High limit switches are calibrated to a specific trip temperature. An incorrect or generic replacement can trip too early — leaving you without heat — or too late, allowing dangerous overheating. The factory-spec 26G78 ensures the exact temperature calibration and terminal configuration your Lennox system was designed around.