Lennox Furnace Flame Sensor FLS52W29 52W29 LB-74940A

Lennox Furnace Flame Sensor — FLS52W29

The ERP FLS52W29 is an aftermarket flame sensor for selected Lennox furnaces with hot-surface ignition systems. It helps the furnace control verify flame during burner operation. A failed, contaminated, or damaged sensor can contribute to ignition lockout, no-heat symptoms, or repeated start attempts. Match the original sensor, length, terminal, ignition system, and complete furnace model before ordering.

ERP aftermarket replacement: This part is not a genuine Lennox part and is not affiliated with Lennox.

Compatible Part Numbers

• FLS52W29
• 52W29
• LB-74940A
• 31L71

Key Features

• Direct replacement: Replaces a compatible HSI furnace flame sensor when specifications and fit match.
• Primary function: Helps the furnace control verify burner flame.
• Key benefit: Helps restore reliable flame proving and heating operation when the original sensor fails.
• Construction and fit: Alumina ceramic insulator, Kanthal flame rod material, 4-7/8-inch overall length, 2-3/4-inch sensor length, 1-1/2-inch base length, and 1/4-inch quick-disconnect termination.

Fixes These Symptoms

• Furnace ignites but shuts down shortly afterward
• Furnace enters ignition lockout or produces no heat
• Repeated ignition attempts or short cycling
• Flame sensor is damaged, contaminated, or corroded

Compatible Brands

• Lennox

Compatible Models

Fits various models. Please verify compatibility with us before ordering.

Always verify your model number before ordering. Match the complete furnace model, original part number, ignition system, sensor dimensions, and terminal. Gas and combustion service must be performed by a qualified HVAC technician.