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The Lennox 11U71 (104371-08) is a genuine OEM furnace pressure switch rated at 0.85" water column, engineered to confirm adequate negative pressure from the inducer motor before enabling the ignition sequence on your Lennox furnace. Common symptoms of a failed pressure switch include furnace lockout, no-heat conditions, and repetitive ignition failure error codes. This direct OEM replacement ensures an exact fit and restores safe, efficient operation in compatible Lennox gas furnace models.