Lingo > Soot
Soot defines itself. The reason it's included here is because it's sometimes and under certain conditions found in the combustion chambers and flues of water heaters -- and it's a bad sign.
If you didn't know that, you might not recognize it when you saw it -- or worry. One telltale is black stuff on the cover of a tank around the draft diverter, below right. Another is a blackened combustion chamber, as above right.
The reason to worry is that soot means a fouled combustion chamber and flues. Gas is not being completely burned. It's a downward spiral that can result in flames billowing out of the bottom of the tank, potentially setting anything nearby on fire.
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