Home Improvement

What causes knocking in drain pipes when hot water drains?

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Wiki User
2006-07-27 14:28:58

materials tend to expand when they get hot, and that is true for

sewer pipe material as well. Whether it's cast iron or ABS, the

pipes will try to expand when they get hot and when they try to get

longer they'll slide across wood or other materials. The "knocking"

noise is the pipe fitting tightly against the wood and when the

pipe has expanded enough it moves suddently and for a short

distance, producing a "pop" type of sound. If you can expose the

pipe you can cut out the wood where it is tight and possibly put in

other material so that the pipe doesn't rub so hard.

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