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The genuine OEM Lennox 75M20 pressure switch is a furnace safety control that confirms correct combustion airflow and venting before the burners are allowed to ignite. Linked by hose to the draft inducer, it monitors negative pressure and closes its contacts only when the inducer establishes proper draft. Each 75M20 is factory-calibrated to the specific pressure set point your Lennox furnace requires for safe operation.
Common failure symptoms: A faulty or tripped 75M20 usually prevents ignition and triggers a diagnostic fault. Look for the inducer motor running without the burners lighting, repeated short cycling, a furnace that ignites then quickly shuts off, or contacts that fail to close. Blocked flue passages, a cracked sensing hose, or condensate buildup commonly cause these problems.
Why OEM matters: Because this switch protects against unsafe venting, using a replacement with the wrong pressure rating risks nuisance lockouts or bypassing an essential safety check. The OEM Lennox 75M20 provides the precise factory calibration, correct port configuration, and reliable contact operation your Lennox furnace was engineered to use, keeping your heating system safe and dependable.