Why is my pilot flame yellow instead of blue?
A yellow pilot flame means it's burning dirty — not getting enough air, or its orifice is partially blocked by dust, lint, or spider webbing. A healthy pilot is crisp blue. Yellow burns cooler and sootier, so it also struggles to heat the thermocouple, which is why it often comes paired with a pilot that won't stay lit.
Blue means clean, yellow means starved
Complete combustion burns blue. When a pilot goes yellow and lazy, it's starved of air or the fuel is being throttled by an obstruction — the flame can't burn cleanly, so it lights up yellow, deposits soot, and runs cooler. That lower temperature matters: the thermocouple and thermopile need a hot, enveloping flame to generate their voltage, so a yellow pilot frequently shows up right before a "won't stay lit" or "won't turn on" call.
Where the blockage comes from
The pilot orifice is a pinhole, and it doesn't take much to choke it. Off-season spider webs, mud-dauber nests, dust, and pet hair are the everyday culprits we pull out of pilot assemblies across Asheville and Hendersonville every fall. On a converted appliance, a yellow flame can also mean the wrong pilot orifice for the fuel — a natural-gas pilot running on propane, or vice versa, burns wrong. Getting the fuel and orifice matched correctly is part of why NG-to-LP conversions are licensed work.
Don't just relight it — clean it
Relighting a yellow pilot gets you the same yellow pilot. The real fix is cleaning the pilot assembly and orifice, confirming air supply, and verifying gas pressure — and because that means opening the sealed gas control, it's work we're licensed to do. It's usually inexpensive and part of a standard tune-up. Book service before heating season and you rarely see this at all. Call (828) 545-0525.
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