Lennox 18G89 Flame Sensor

The Lennox 18G89 Flame Sensor is a critical OEM replacement part designed to maintain the safety and operational integrity of residential and commercial gas furnaces. This straight-style sensor, also identified by part number 18G8901, acts as the primary safety mechanism by providing continuous microamp signal detection to the integrated furnace control board. Engineered with a durable Kanthal D or Hoskins 815 electrode and a glazed L-5 Steatite ceramic insulator, it is built to withstand high-temperature combustion environments while preventing carbon buildup that leads to nuisance lockouts. As a veteran technician, you know that a faulty flame sensor is a leading cause of the "ignition for 3 seconds then shutdown" symptom. Maintaining a clean 13/16 inch sensing element is vital for system-wide HVAC safety. This genuine component replaces several legacy part numbers including 65206300 and LB-74940A, ensuring a precise fit for Lennox G12, G16, G20, and G23 series furnaces, as well as Allied and Armstrong units.

• Universal Compatibility: Direct drop-in replacement for Lennox 18G8901 and older Armstrong/Ducane furnace flame sensors.
• High-Temperature Durability: Constructed with industrial-grade Kanthal D alloy to resist oxidation and thermal stress during long heating cycles.
• Optimized Conductivity: Features a nickel-plated steel male terminal for reliable electrical continuity and accurate flame rectification.
• Precision Insulation: Glazed ceramic base prevents high-voltage leakage, ensuring the furnace control board receives a clean signal.

How do I diagnose a failing Lennox 18G89 Flame Sensor?
If the burners ignite but extinguish within 2 to 5 seconds, it often indicates the sensor is unable to send a sufficient microamp signal. Check for cracks in the ceramic insulator or significant carbon deposits on the rod before replacing.

Is the 18G89 interchangeable with the 18G8901?
Yes, the 18G89 is technically identical to the 18G8901 part number; they are the same physical component and can be used interchangeably in all listed Lennox and Allied Air models.

What causes these sensors to fail prematurely?
While they are designed for longevity, poor combustion air quality, high humidity, or use of abrasive cleaning materials can degrade the sensing rod’s surface, eventually requiring a full replacement to restore reliable ignition.

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.