Description
The Lennox 21L99 is an OEM replacement flame sensor designed to deliver dependable flame detection and safe furnace operation in compatible Lennox gas heating systems. Flame sensors are a critical safety component — they verify that a flame is present after the ignition sequence initiates, preventing unburned gas from accumulating and ensuring your system operates safely and efficiently.
Why Replace Your Flame Sensor?
Over time, flame sensors accumulate oxidation and carbon buildup on the sensing rod, causing the furnace control board to lose confidence in the flame signal. This leads to nuisance lockouts, short cycling, and no-heat calls. Replacing the sensor with a genuine Lennox OEM part restores proper microamp signal readings and eliminates these issues.
Key Features
- Genuine Lennox OEM replacement part (SKU: 21L99)
- Engineered for precise flame current detection in compatible Lennox gas furnaces
- Helps prevent nuisance lockouts caused by weak or erratic flame signals
- Direct drop-in replacement — no modification required
- Restores safe and reliable furnace ignition performance
- Manufactured to Lennox quality and performance standards
Application
The Lennox 21L99 Flame Sensor is intended for use in compatible Lennox gas furnace models. Always verify compatibility with your specific unit’s model and serial number before installation. Consult the furnace service manual for proper torque specifications and microamp testing procedures after installation.
Installation Notes
- Disconnect power before servicing
- Clean the sensor mounting bracket area before installing the new sensor
- Verify flame current reading (typically 1–10 microamps DC) after installation using a multimeter in series with the sensor lead
- Ensure the sensing rod is properly positioned in the burner flame envelope
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