Lennox 79J22 Flame Sensor

As a seasoned tech, you know that a flickering signal or a nuisance lockout on a Lennox furnace often traces back to a fouled or failing 79J22 flame sensor. This genuine OEM Lennox part (also referenced as PSE-L18) is a critical safety component designed to verify flame rectification. When the burner ignites, this sensor must detect the microamp signal to hold the gas valve open; if the ceramic insulator is cracked or the stainless steel rod is excessively oxidized, the control board will drop the call for heat, leading to repeated short cycling or a permanent furnace lockout. This Lennox replacement flame sensor is engineered for high-temperature durability and precision fitment in specific GCS and LGA series units. Whether you are performing a seasonal tune-up or a mandatory repair, swapping out a degraded sensor with this 79J22 ensures reliable ignition sequences and prevents hazardous gas buildup by confirming every burner cycle.

• Direct OEM Replacement: Ensures exact electrical compatibility with Lennox control boards, providing the correct microamp (µA) feedback signal.
• High-Temperature Resistance: Constructed with a durable ceramic insulator and a robust metal rod to withstand the intense heat of the combustion chamber.
• Critical Safety Function: Prevents the gas valve from remaining open if a stable flame is not detected, protecting the heat exchanger and the property.
• Reduced System Downtime: Resolves common "ignition failure" codes and lockout conditions caused by cracked or worn sensors.

How do I troubleshoot an ignition failure that might be the 79J22?
Check for furnace diagnostic codes. If the burners ignite for 2-5 seconds and then shut off, measure the microamp signal with your multimeter in series. If the reading is below the manufacturer's threshold (typically 1.0 µA), inspect the 79J22 for soot, cracks in the porcelain, or a loose wire connection.

Can I just clean the flame sensor instead of replacing it?
While cleaning a dirty flame sensor with fine abrasive can temporarily restore the signal, repetitive oxidation or a hairline crack in the ceramic insulator requires a full Lennox 79J22 replacement to ensure long-term reliability and system safety.

What models is this sensor compatible with?
The Lennox 79J22 is used in various rooftop units and furnaces, including several GCS16, GCS20, and LGA series residential and commercial models. Always verify against your specific unit's parts list before installation.

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.