OEM Lennox Furnace Pressure Switch — 27W17

The 27W17 is a genuine OEM Lennox furnace pressure switch. This is a critical safety control that confirms the draft inducer is running and that the venting system is clear before the furnace is allowed to ignite. By sensing the negative pressure created by the inducer, the switch proves proper combustion airflow and protects your home from unsafe flue conditions and carbon monoxide buildup.

Common failure symptoms: the furnace locks out and won't light, the inducer runs but ignition never begins, short-cycling on a call for heat, or a control-board fault code indicating an open or stuck pressure switch. A failed or contaminated switch, a cracked hose, or a blocked pressure tap will all keep the furnace from firing.

Why OEM matters: pressure switches are calibrated to a precise trip point (measured in inches of water column) that is matched to your specific Lennox furnace and inducer. The factory 27W17 carries the exact setpoint, port configuration, and terminals your unit expects, so it proves draft correctly and keeps the safety circuit reliable. A mis-rated aftermarket switch can nuisance-trip or fail to prove — install the genuine Lennox part for safe, code-correct operation.