OEM Lennox Pressure Switch — 36W49

The genuine OEM Lennox 36W49 pressure switch is a safety control that confirms proper draft and airflow before your Lennox furnace is allowed to ignite. As the inducer motor starts, it creates negative pressure sensed through the switch's port; the 36W49 must close to prove that combustion gases will vent safely and that the flue is not blocked. Only after this proving signal reaches the control board will the ignition sequence continue — making the switch a critical link in safe furnace operation.

Common failure symptoms: a faulty or tripped pressure switch typically stops ignition and triggers a lockout, often shown as a specific flash code. Symptoms include a furnace that runs the inducer but never lights, short cycling, and no heat. Note that a stuck-open switch can also be signaling a real problem — a blocked flue, cracked hose, condensate-clogged port, or failing inducer — so verify airflow before replacing.

Why OEM matters: pressure switches are calibrated to a precise trip point in inches of water column specific to your Lennox model. An aftermarket switch with the wrong setpoint may fail to prove or, worse, prove when it shouldn't — defeating a safety function. The factory 36W49 guarantees the correct calibration and fit for safe, code-compliant operation.