OEM Lennox Limit Switch — 33J34

The genuine OEM Lennox 33J34 limit switch is a high-limit safety control for Lennox furnaces. Positioned to read the temperature of air moving across the heat exchanger, it automatically de-energizes the burner or heating element if the furnace overheats, protecting the heat exchanger and preventing unsafe operating conditions. The 33J34 is calibrated to the precise trip and reset temperatures Lennox specifies for your equipment.

Common failure symptoms include short cycling, burners that ignite then shut off almost immediately, a blower that never stops, no heat on a call, or a limit-fault lockout on the control board. A limit switch that has drifted out of calibration will trip early and interrupt heating, while one that fails closed eliminates a key safety safeguard.

Why OEM matters: as a safety-critical control, the 33J34 must match its exact temperature ratings, terminal configuration, and mounting to function correctly. Generic replacements with different trip points can cause nuisance shutdowns or allow dangerous overheating. The factory Lennox part restores proper protection and reliable performance for your system.