OEM Lennox Pressure Switch — 26W86

The genuine OEM Lennox 26W86 pressure switch is a critical safety control that confirms your Lennox furnace is drafting and venting properly before the gas valve is allowed to open. It senses the negative pressure created by the inducer motor and closes its contacts only when airflow is adequate, preventing ignition under unsafe venting conditions.

A failing pressure switch typically shows up as a furnace that ignites briefly then shuts down, a unit that won't fire at all, or a repeating lockout with the inducer running but no flame. Common causes include a stuck diaphragm, clogged sensing tubing, water in the port, or contacts that no longer close reliably — all of which the furnace control board reads as a venting fault.

Because Lennox calibrates each pressure switch to a specific trip point matched to the furnace's inducer and venting design, installing the correct OEM 26W86 is essential. A switch with the wrong pressure rating can allow the burner to fire when venting is inadequate or cause nuisance lockouts on a healthy system. The factory part guarantees the exact set point, preserves your warranty, and keeps this safety circuit working as engineered.