OEM Lennox Dual Pressure Switch Assembly — 18M63

The genuine OEM Lennox 18M63 dual pressure switch assembly is a combustion-air safety control that proves proper venting before and during furnace operation. Sensing negative pressure created by the draft inducer, its two switches confirm that flue gases are being safely drawn out and that the vent is not blocked, allowing the ignition sequence to proceed only when conditions are safe. On two-stage furnaces, the dual design verifies draft at both firing rates.

When the 18M63 fails or its ports and tubing clog, you'll often see the furnace fail to ignite, lock out on a pressure-switch fault, short-cycle, or display a related error code from the control board. Cracked tubing, a stuck diaphragm, condensate in the hose, or a blocked vent are common causes of a switch that won't close — or one that won't open when it should.

Choosing the OEM Lennox 18M63 matters because pressure switches are calibrated to a specific trip point measured in inches of water column for your exact furnace model and vent configuration. A switch with the wrong rating can allow unsafe operation or cause persistent nuisance lockouts. This factory-matched assembly restores accurate draft proving and reliable ignition for your Lennox equipment.