OEM Lennox Dual Pressure Switch Assembly — 40W05

The genuine OEM Lennox 40W05 dual pressure switch assembly provides two-stage draft verification for high-efficiency and two-stage Lennox furnaces. Each switch confirms proper venting pressure at its respective firing rate, allowing the control board to safely stage the burners up and down for optimal comfort and efficiency.

When one or both switches in the 40W05 assembly fail, or when the sensing tubes become obstructed by condensate or debris, the furnace may refuse to ignite, get stuck on low fire, short cycle, or report a pressure-switch fault. Because the assembly governs both heating stages, a fault can compromise the unit's ability to modulate output correctly.

Installing the OEM assembly is critical for two-stage systems, where each switch is calibrated to a distinct pressure setpoint tuned to your Lennox model's venting design. Generic single-stage substitutes cannot replicate this dual-threshold logic and can lead to unsafe operation or persistent lockouts. The factory 40W05 assembly restores full two-stage functionality, safe venting, and the efficiency your Lennox furnace was engineered to deliver.