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The genuine OEM Lennox 20J97 pressure switch is a critical safety component in your Lennox furnace. It monitors negative pressure created by the draft inducer to confirm proper venting and combustion airflow before the ignition sequence begins. If the switch does not sense adequate draft, it prevents the furnace from firing to protect against dangerous flue gas spillage.
Common failure symptoms: When the 20J97 fails or sticks, you may experience a furnace that ignites and then shuts off, no heat with the blower running, repeated lockouts, or a control board flashing a pressure switch fault code. Cracked hoses, a stuck diaphragm, or contact fatigue are typical culprits.
Why OEM matters: Lennox calibrates each pressure switch to a specific trip point (measured in inches of water column) matched to your furnace model. An off-spec aftermarket switch can trip early, fail to prove draft, or bypass a safety it was designed to enforce. Choosing the factory 20J97 guarantees the correct set point, proper fit, and reliable, code-compliant operation season after season.