OEM Lennox Limit Switch — 18K43

The genuine OEM Lennox 18K43 limit switch is an essential safety device in your Lennox heating system. It monitors the temperature around the heat exchanger and opens the burner circuit whenever heat exceeds the safe threshold, preventing damage from overheating and restoring operation once conditions cool. This direct factory replacement delivers the exact fit and calibrated trip point your furnace requires.

Common failure symptoms: When the 18K43 goes bad, typical signs include the furnace failing to produce heat, short-cycling on and off, the blower motor running continuously, or the system locking out after repeated trips. A limit switch that opens too early causes frustrating intermittent heating, while one stuck closed removes a vital layer of protection.

Why OEM matters: Lennox designs each limit switch, including the 18K43, with a precise temperature rating suited to its specific furnace platform. Off-brand parts with mismatched thresholds can trigger false shutdowns or leave your equipment unprotected. The authentic OEM component restores the exact safety behavior Lennox intended, keeping your furnace operating safely and efficiently for years to come.