OEM Lennox Limit Switch — 29M75

The genuine OEM Lennox 29M75 limit switch is a temperature-sensing safety control that monitors heat inside your Lennox furnace. If the plenum temperature climbs above a safe threshold — typically due to restricted airflow — the switch opens to shut off the burners, preventing overheating and protecting the heat exchanger from damage. It's a small but critical safety device in the furnace's control sequence.

Common failure symptoms include a furnace that short cycles (burners igniting then quickly shutting off), no heat, the blower running continuously, or repeated safety lockouts. A limit switch can fail open (blocking ignition entirely) or fail closed (defeating its protective function), so accurate testing is important before replacement.

Why OEM matters: the Lennox 29M75 is set to the precise temperature trip point and physical dimensions your furnace model requires. A mismatched aftermarket switch may trip too early, too late, or not at all — compromising both comfort and safety. Installing the correct OEM limit switch restores proper protection and reliable heating. Always disconnect power before servicing, and address any underlying airflow restriction, such as a dirty filter or blocked ducts, that may have caused the switch to trip.