{"product_id":"oem-lennox-pressure-switch-51w91","title":"OEM Lennox Pressure Switch — 51W91","description":"\u003cp\u003eThe Lennox \u003cstrong\u003e51W91\u003c\/strong\u003e pressure switch is a combustion-airflow safety control that confirms proper venting in your Lennox furnace prior to ignition. When the inducer motor starts, it produces a negative pressure that the \u003cstrong\u003e51W91\u003c\/strong\u003e detects through its sensing port. The switch closes only when sufficient draft is present, allowing the ignition sequence to continue and preventing operation when the flue or vent is obstructed.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCommon failure symptoms:\u003c\/strong\u003e If the \u003cstrong\u003e51W91\u003c\/strong\u003e fails, you'll often see the inducer spin up while the burners never fire, along with a pressure-switch error on the diagnostic board. Symptoms include short-cycling, intermittent no-heat calls, and repeated lockouts. A stuck diaphragm, blocked or cracked tubing, or a switch that has drifted out of calibration are typical causes.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhy OEM matters:\u003c\/strong\u003e The \u003cstrong\u003e51W91\u003c\/strong\u003e is factory-set to the precise pressure specification your Lennox furnace demands. Aftermarket switches with incorrect set points may refuse to close or, dangerously, close when they shouldn't — bypassing a genuine venting fault. Installing the authentic OEM \u003cstrong\u003e51W91\u003c\/strong\u003e ensures accurate calibration, proper fit, and complete compatibility with your Lennox equipment.\u003c\/p\u003e","brand":"Lennox","offers":[{"title":"Default Title","offer_id":63081103688051,"sku":"LNX-51W91","price":24.95,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0984\/1190\/5395\/files\/nhvac-pressure-switch-single-LNX-51W91.jpg?v=1783763049","url":"https:\/\/nationalhvacparts.com\/products\/oem-lennox-pressure-switch-51w91","provider":"National HVAC Parts","version":"1.0","type":"link"}