Lennox 33F37 Flame Sensor

The Lennox 33F37 Flame Sensor is a critical OEM replacement part engineered to maintain the safety and operational sequence of residential gas furnaces. As an HVAC flame rectification probe, it generates a microamp signal to the furnace control board upon detecting heat, ensuring the gas valve remains open only when a pilot or burner flame is present. This high-integrity sensor is functionally identical to part 33F3701 and serves as a direct replacement for several legacy Lennox furnace parts, including 73A59, 28C27, and 26F17. Built with a high-temperature ceramic insulator and a durable Kanthal flame rod, the 33F37 is designed to withstand the harsh environment of the burner assembly while providing millisecond response times to prevent ignition lockout. Technical professionals frequently utilize this furnace flame sensor to resolve common short-cycling issues and E240 error codes across multiple Lennox G11, G12, and G8 series units. Its precision alignment ensures consistent flame signal reliability for both single-stage and two-stage heating configurations.

Key Benefits

• Ensures safe furnace operation by monitoring for flame rectification and preventing hazardous unburned gas accumulation.
• Features OEM compatibility with legacy Lennox and Allied Air models, directly replacing part numbers 33F3701 and 73A5901.
• Constructed with a heavy-duty sensing electrode to resist carbon buildup and oxidation under high thermal stress.
• Facilitates rapid HVAC troubleshooting for systems experiencing furnace ignition failure or repeated lockout cycles.
• Designed for precise fitment in the air gas plenum, allowing for straightforward field replacement without burner removal on most models.

Common Questions

What are the symptoms of a failing Lennox 33F37 flame sensor?
The most common indicator is when the furnace burners ignite but shut down within 2 to 5 seconds. This typically results from the sensor failing to send a sufficient microamp signal to the control board, triggering a safety shutdown.

Is the 33F37 interchangeable with the 33F3701?
Yes, the 33F37 is identical to 33F3701. These part numbers are used interchangeably by the manufacturer and share the same technical specifications, dimensions, and mounting brackets.

Can this sensor be cleaned instead of replaced?
While light oxidation can sometimes be removed with a fine abrasive like emery cloth, a cracked ceramic insulator or a severely pitted flame rod requires a full OEM sensor replacement to ensure the system meets factory safety standards.

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.