Hi all,

We have a 75 gallon, 75,100 BTU natural gas water (State Industries,
"Select" model) that probably is seven years old. I routinely drain water
off the bottom valve to flush out any sediment.

Lately I have noticed that when burner is on, it "clunks" and "knocks"
noticeably (a louder version of what a tea kettle sounds like on the stove).

I assume that it is water boiling near the flames, but thought it might be
due to excessive calcium build-up at the bottom of the tank, "insulating"
the bottom of the tank from the heat.

Anyway, is noticeable "knocking" when the burner is on an indication of
pending failure, or is there anything else I should in response to these
symptoms. Thank you.

Best,

doug