Lennox 39F95 Flame Sensor

The Lennox 39F95 Flame Sensor is a critical OEM safety component engineered for precise flame rectification in gas-fired heating systems. This furnace flame sensor replacement is a direct-fit for many Lennox, Armstrong, and Ducane units, including popular models like the G11 and G12 series. Designed with a 1-inch element length and a 0.114-inch diameter probe, it monitors the burner's ionized flame to provide the necessary microamp (µA) signal to the integrated furnace control. This genuine Lennox part (also identified as 39F9501) ensures the gas valve remains open only when a stable ignition is detected, preventing hazardous unburned gas accumulation.

For service technicians performing HVAC troubleshooting, a failed flame sensor is a common cause of short-cycling or ignition lockout. This sensor utilizes a durable ceramic insulator and a high-grade stainless steel rod to withstand constant thermal cycling. When testing with a digital multimeter in series, a healthy Lennox 39F95 should typically register between 2.0 and 7.0 microamps. If your reading drops below 2.0 µA, or if the sensor shows signs of heavy carbon buildup or a cracked insulator, replacing it with this OEM replacement part is the industry-standard fix to restore reliable furnace operation.

• OEM Compatibility: Precision-matched for Lennox, Armstrong, Concord, and Ducane HVAC systems to ensure internal reference patterns are met without component mismatch.
• Enhanced Safety: Provides immediate flame verification to prevent gas valve malfunctions and potential combustion hazards.
• Durable Construction: Built with high-temperature materials and an 18 AWG lead wire to ensure longevity in the burner's high-heat environment.
• Direct Replacement: Interchangeable with part number 39F9501 and cross-references with 37C51 and 37C5101 for versatile field application.

What are the symptoms of a bad Lennox 39F95 flame sensor?
Common signs include the furnace lighting and then shutting off after a few seconds, or the system entering a hard lockout state after three failed ignition attempts. Technicians should check for a low microamp signal at the control board.

Can I clean the 39F95 sensor instead of replacing it?
While light oxidation can sometimes be removed with very fine steel wool, a sensor with a cracked ceramic insulator or deep pitting must be replaced to ensure the safety circuit remains intact and grounded properly.

How do I test the flame signal on this part?
Set your multimeter to the DC microamp (µA) scale and connect it in series between the flame sensor terminal and the control board wire. A standard reading for this OEM probe is typically in the 2.5 to 6.0 µA range once the flame is established.

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.