Posted by Don, From: on October 29, 1999 at 15:57:08:

In Reply to: Knocking sound - Water Heater - HELP! posted by Mike H. on October 28, 1999 at 18:36:00:

Boiling, knocking sounds from the water heater usually mean it has a lot of lime build up inside. Something about the water boiling under the lime or whatever, I really don't know...But I see it a lot here (the water is hard).
You can try to clean it out, or replace the heater, or live with it. I never saw a heater get damaged by the knocking.

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