Description
Lennox 12L09 Flame Sensor Overview
The Lennox 12L09 Flame Sensor is a genuine OEM replacement component designed to deliver dependable flame detection in compatible Lennox furnace systems. The flame sensor plays a critical safety role in your heating system — it proves that a burner flame is present and signals the control board to keep the gas valve open. A failed or fouled flame sensor is one of the most common causes of furnace short-cycling and no-heat calls, making this a go-to replacement part for HVAC technicians and service professionals.
Key Features
- OEM Lennox replacement flame sensor — SKU 12L09
- Designed for precise fit and function in compatible Lennox furnace models
- Detects burner flame via electrical current rectification to prove ignition
- Helps prevent unsafe furnace operation by shutting down gas flow when no flame is detected
- Durable construction for long service life in demanding heating environments
- Direct replacement eliminates guesswork and reduces installation time
Application
The 12L09 flame sensor is intended for use in select Lennox gas furnace models. Always verify compatibility with the specific furnace model number before installation. Consult the equipment’s service manual or the Lennox parts cross-reference guide to confirm fitment.
Why Replace Your Flame Sensor?
Over time, flame sensors accumulate oxidation and carbon deposits on the sensing rod, which reduces the microamp signal sent back to the control board. When the signal drops below the board’s threshold, the furnace will lock out on a safety fault — typically after 2–3 ignition attempts. Replacing the flame sensor restores proper microamp readings and eliminates nuisance lockouts.
Installation Notes
- Always disconnect power before servicing
- Handle the sensing rod carefully — avoid touching with bare hands
- Secure the mounting bracket firmly to ensure proper positioning in the burner flame
- Verify microamp signal with a multimeter after installation to confirm proper operation
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