OEM Lennox Flame Sensor — 17J56

Genuine OEM Lennox 17J56 flame sensor. This component verifies that a flame is present after ignition by generating a small flame-rectification current, telling the furnace control board it is safe to keep the gas valve open. It is a core safety device in your Lennox gas furnace and directly controls reliable, uninterrupted heating.

Common failure symptoms: When the 17J56 becomes coated with oxidation or carbon, or cracks with age, the burners light and then shut off after a few seconds — a classic short-cycling or "clicks then no heat" complaint. You may also see repeated ignition lockouts, weak or intermittent flame confirmation, and error codes pointing to loss of flame signal.

Why OEM matters: Lennox flame sensors are calibrated to the exact microamp signal range the furnace control board expects. An aftermarket rod with the wrong length, alloy, or mounting geometry can read a false weak signal and trigger nuisance lockouts even when the flame is healthy. Installing the factory 17J56 guarantees correct fit, proper flame-rod positioning, and the rated signal strength your Lennox equipment was engineered around — restoring dependable, safe furnace operation.