Yellow flame during cold tank start?

Discussion in 'Water Heater Forum, Tanks' started by Runs with bison, Aug 29, 2009.

  1. Runs with bison

    Runs with bison Member

    Aug 23, 2009
    Upon completing my recent water heater gas thermostat replacement I watched the start up carefully from the floor peering into the window. Everything started up fine, pilot lit cleanly with a blue flame, and the burner lit cleanly with a nice blue flame. All appeared normal.

    The tank was full of cold water. After a minute or so the flame abruptly turned yellow all the way around the burner. I watched for a few seconds then shut it down and rechecked everything. I noticed some condensate dripping down the central chimney pipe inside the water heater. I restarted the pilot, again a nice blue. But again the burner started up with a robust yellow flame. I adjusted the thermostat setting back and forth a few times to the point of shutting off the flame if memory serves, but the yellow flame persisted.

    Since the new CO monitor was not alerting, there was no soot, no smell, and no evident problem with the draft I let the burner run while continuing to observe. (I used to work with syngas reactions frequently so I'm respectful of CO.) Condensate was dripping steadily down the walls of the inner chimney and falling onto the burner pan. This lasted for several minutes. Eventually the tank contents warmed, the condensate drip ceased, and the burner color went back to its normal blue. I've checked it during operation several times since and the flame has a normal blue appearance every time.

    So the question: is this yellow flame normal/not unexpected when the tank is so cold that the burner is acting as a condensing gas water heater? I suspect that if the condensate was channeled away from the burner, the flame would have remained blue and the start up would have been at 90+% thermal efficiency vs. 78-80% normal thermal efficiency for non-condensing mode.
  2. curlysir

    curlysir New Member

    Sep 21, 2009
    Mine did the same thing today when I started it up from a full cold start.
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  4. jdgoodman

    jdgoodman Journeyman Plumber

    Sep 14, 2009
    This is normal when firing up a heater.
  5. Master Plumber Mark

    Master Plumber Mark Sensitivity trainer and plumber of mens souls

    Feb 6, 2005
    Sensitivity trainer.. and plumber of mens souls
    indianapolis indiana - land of the free, home of


    and yellow is a pretty color....
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