{"product_id":"oem-lennox-flame-sensor-33f37","title":"OEM Lennox Flame Sensor — 33F37","description":"\u003cp\u003eThe genuine OEM Lennox \u003cstrong\u003e33F37\u003c\/strong\u003e flame sensor confirms that a flame is present after the burners ignite. Using flame rectification, it sends a small electrical signal to the control board proving combustion has been established. If the board doesn't detect this signal within seconds, it shuts off the gas valve to prevent a dangerous buildup of unburned fuel — making the sensor a key safety component of every heating cycle.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCommon failure symptoms\u003c\/strong\u003e include a furnace that lights briefly then shuts off, repeated short cycling on ignition, the system going into lockout after several failed attempts, or no heat despite the igniter glowing. A dirty, corroded, or cracked flame sensor is one of the most frequent causes of intermittent furnace operation.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhy OEM matters:\u003c\/strong\u003e The \u003cstrong\u003e33F37\u003c\/strong\u003e is built with the exact rod length, mounting, and material Lennox requires for a reliable flame-rectification signal. A genuine factory sensor ensures consistent detection and proper positioning in the flame. Aftermarket sensors may sit incorrectly or generate a weak signal, leading to nuisance lockouts. Install the OEM \u003cstrong\u003e33F37\u003c\/strong\u003e for safe, dependable ignition and steady heat.\u003c\/p\u003e","brand":"Lennox","offers":[{"title":"Default Title","offer_id":63081109160307,"sku":"LNX-33F37","price":19.95,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0984\/1190\/5395\/files\/nhvac-flame-sensor-straight-LNX-33F37.jpg?v=1783761022","url":"https:\/\/nationalhvacparts.com\/products\/oem-lennox-flame-sensor-33f37","provider":"National HVAC Parts","version":"1.0","type":"link"}