Definition
A flame sensor is a thin metal rod positioned in a gas furnace's burner flame that confirms ignition by passing a tiny electrical current through the flame, a process called flame rectification. If the control board does not detect that signal within seconds, it closes the gas valve as a safety measure. A dirty sensor causes nuisance shutdowns.
Also called: Flame rod, Flame sensing rod
Why it matters to you
A sooty or oxidized flame sensor is one of the most common reasons a furnace lights, runs for a few seconds and then shuts off, often on the first cold nights of fall. Through a long SW Washington and Portland-metro heating season a furnace lights many times a day, so sensor buildup is a routine maintenance item.
Practical guidance
If the furnace repeatedly lights and drops out, note any blinking code on the control board's indicator light and call for service rather than resetting it over and over. Cleaning or replacing the flame sensor means working in the burner compartment and is technician work, typically part of a fall heating tune-up.
About this definition
Written by the Home Energy Group team — a family-owned HVAC company celebrating 25 years of comfort & care across SW Washington and the Portland metro, licensed in Washington (WA LIC# HOMEEGI003J7) and Oregon (OR CCB# 184255). Definitions inform; an on-site diagnosis decides.
