OEM Lennox Two-Stage Gas Valve — 21W04

The genuine OEM Lennox 21W04 gas valve, also identified by part number 101019-01, is a two-stage gas valve that meters fuel to the burners of compatible Lennox furnaces at two distinct firing rates. By modulating between low and high stage, it delivers quieter, more efficient heating during mild conditions and ramps up to full capacity when the thermostat calls for more heat.

Signs that the 21W04 may need replacement include the furnace not lighting, ignition only on one stage, delayed or noisy ignition, short cycling, flickering or uneven flame, or a valve that clicks but fails to open. Because it is a two-stage component, a failure often shows up as the system being unable to reach or hold the higher heating stage.

An OEM Lennox 21W04 valve is calibrated to the exact manifold pressure, gas type, and 24V control signals your furnace requires. Since gas valves are precision safety devices, using the genuine factory part ensures correct staging, clean combustion, dependable operation, and full compliance with your Lennox equipment's safety ratings — assurance that aftermarket alternatives cannot reliably match.