Hi. I have annoying loud knocking sounds coming from a 3 inch diameter hot water pipe that feeds part of the 23 story apartment building that I live in. It feeds each apartment's heat register ( a 1 inch pipe coming off the 3 incher)Management can't figure out the problem. Only a few apartments experience this sound. I opened up the wall in my apartment out of desperation to see what I could see. (I thought maybe a small leak but no, no leak). This pipe is surrounded by concrete and there is no gap (to allow for expansion) between the pipe and concrete. My question is: Would drilling some 1/4 inch "relief holes" in the concrete surrounding the pipe relieve the pressure and allow for better contracting/expanding and hopefully end the knocking? Thanks for a reply.

Sincerely,

John

Among others, the knocking noise in hot water pipes can be caused by Thermal Expansion. It could also be caused by friction as pipe expands and contrast. If you have hot water circulation pump installed on the system than inspect it for proper operation.

To solve Thermal Expansion problem, install Thermal Expansion tank. To relieve friction, loosen pipes.