Black Carbon Residue on Outside of Older Water Heater

The Tank Black Carbon Residue on Outside of Older Water Heater

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    I have a gas water heater that is over 15 years old. At the bottom around the hole where the pilot light is there is alot of black carbon like residue and also on the top where the vent to the outside is. The home inspection guy said that it is very dangerous but did not say how to fix it. He marked it off of the inspection because he did not want to stop us from buying the house. Can anyone tell me what it is from and how to fix it? My email address is


    Black carbon is an indication of too little oxygen (air) in the flame. Check for a mixing body where the gas jet draws in combustion air. If the flame is yellow, you need to increase the area available for the air. Flame should be blue. A yellow flame also produces more carbon monoxide. It looks like this is a new house for you. Any home which burns fossil fuels should not be without carbon monoxide detectors.



    Thank you so much for the reply. This is our 1st home. My parents are the previous owners which helps some. They are tight with their money and don’t want to replace the heater. My Dad keeps saying don’t worry about it, but the inspector said it is very dangerous. We do have a CO2 alarm about 3 yards from it. I have been searching the internet for answers. What would you say to do to fix the problem?

    Larry Weingarten

    Hello: Soot build-up tells you there was a problem with air getting to the burner. This could either be a problem with air coming or going. A blocked flue or exhaust fan pulling air down the vent pipe are common causes of trouble. Once soot starts to build up, it quickly makes the problem worse. It could be a messy job, but vacuuming out the combustion chamber, removing the flue baffle and washing it and making sure there is a good clean air supply to the heater are in your future 😎

    Once everything is quite clean and you’ve checked for anything that could prevent good venting or air supply, light up the heater and see how it does. Expect it to be quite yellow for a few minutes, but then hopefully the flame will turn blue. Propane heaters are more likely to soot up than natural gas. Also, the heater certainly needs a new anode to keep it going. Otherwise your efforts could soon be for nothing as heaters usually don’t last fifteen years. Do make sure both combustion chamber hatch covers are in place.

    One more thought; when you clean out the combustion chamber, look for any evidence of rusting or leaks. If there is heavy rust or any water other than condensation, you’ll want a new heater 😕

    Yours, Larry

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