Lennox 20J91 Flame Sensor

Replace your worn or fouled Lennox 20J91 with this authentic Lennox Flame Sensor to ensure reliable flame rectification and consistent ignition cycles. As a veteran-grade OEM furnace replacement part, this sensor is engineered to provide precise microamp signal feedback to the furnace control board, preventing safety lockouts and intermittent heating failures. The 20J91 is functionally identical to the 20J9101 and serves as a direct-fit component for a wide range of Lennox gas furnaces and unit heaters, including the G25 and LF24 series. If you are troubleshooting a furnace starting then stopping after a few seconds, the high-temperature stainless steel rod and ceramic insulator on this furnace flame sensor are designed to withstand the harsh environment of the burner assembly while maintaining the dielectric strength necessary for accurate flame proving.

Key Benefits:

• Direct OEM Replacement: Fully compatible with Lennox, Air-Flo, and Ducane equipment, specifically replacing part numbers 20J9101 and 20516001.
• Precision Engineering: The L-shaped rod design ensures optimal placement within the flame envelope for a stable flame sensor microamp reading.
• System Safety: Critical for a functional flame proving circuit, effectively preventing hazardous unburned gas accumulation by signaling the gas valve to close when no flame is detected.
• Contractor Grade: Durable alumina ceramic insulator prevents electrical leakage to ground, ensuring the signal reaches the integrated furnace control (IFC).

Common Questions:

How do I know if my Lennox 20J91 flame sensor is bad?
The most common symptom is the furnace burners igniting for 3 to 10 seconds and then immediately shutting down. You can verify this by measuring the DC microamps (µA) in series with the sensor wire; a reading below the manufacturer's threshold (typically 1.0 µA) indicates a fouled or failing sensor.

Is the 20J91 compatible with my unit heater?
Yes, this part is used extensively in Lennox LF24 and TUA series unit heaters, as well as residential G20, G25, and CGHA models. Always verify the part number against your technical manual.

Can I clean the sensor instead of replacing it?
While cleaning with a fine abrasive pad can temporarily remove carbon buildup or silica coating, an HVAC flame sensor with a cracked ceramic insulator or significant pitting on the rod should always be replaced to ensure long-term reliability and safety.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.