OEM Lennox Pressure Switch w/ Bracket — 34M74

The 34M74 is a genuine OEM Lennox pressure switch supplied with its factory mounting bracket. This safety switch monitors the negative pressure created by the inducer/draft blower and confirms that combustion air and flue venting are flowing correctly before the furnace allows the igniter and gas valve to fire. It is a critical combustion-air-proving safety control on your Lennox furnace.

Common failure symptoms: A furnace that ignites briefly then shuts down, the inducer motor running but the burners never lighting, or a control-board fault code indicating an open or stuck pressure switch. A failed switch, cracked hose, or blocked port prevents the system from proving draft, locking the furnace out on safety to protect against a blocked vent or flue.

Why OEM matters: Pressure switches are calibrated to a specific trip point (in inches of water column) matched to your Lennox furnace model and venting configuration. An incorrect or aftermarket switch with the wrong setpoint may fail to prove draft or, worse, allow firing under unsafe venting conditions. The exact OEM 34M74 switch and bracket ensure the correct pressure calibration, secure mounting, and safe, code-compliant operation.