OEM Lennox Limit Switch — 18J28

The genuine OEM Lennox 18J28 limit switch is a temperature-sensing safety device that guards your furnace against overheating. It continuously monitors heat exchanger and supply-air temperatures, and opens the control circuit to shut down the burners if conditions exceed the factory-rated limit. This prevents heat exchanger damage and eliminates a serious fire and safety hazard.

Typical symptoms of a bad 18J28 include the furnace cutting out before reaching the thermostat setpoint, frequent short-cycling, no heat with a high-limit lockout code, or the blower running continuously. Restricted airflow from a dirty filter can accelerate wear, but a switch that has drifted out of calibration must be replaced.

OEM matters here because the 18J28 is calibrated to a specific open/close temperature and built with the correct terminal configuration and mounting for your Lennox model. Off-brand replacements often carry incorrect setpoints that lead to nuisance trips or, dangerously, delayed shutdown. The factory part guarantees exact fit and rated protection, keeping your Lennox system safe and running as designed.