Recently I bought a 13 year old house, and realized that whenever I use hot water upstairs (after I turn off the faucet), I hear thumping sounds every 2 or 3 minutes for about 2 hours. At first, I thought this is water hammer. I closed main water line, drained all water out of pipes, and turned back on. It did not help. I tried emptying water pipes again to see if I still hear thumping sounds when the water pipes are completely empty. I closed main water line, and drained all the water pipes in the house, but I still hear thumping sounds. And.. now I am confused.. can water hammering can happened when there is no water in water pipes? A plumber who visited my house today thinks contracting copper pipes are making this noise, and recommend to install water circulating pump so that copper pipes stays the same size. However, the sounds is not ticking sounds or popping sounds, it is more like thumping sounds when somebody hit pipes with a hammer.Is it possible that the water heater cause thumping sounds since I hear noisy just when I use hot water?

Expansion/contraction of piping is causing the noise. Do you know if you have plastic drain piping? Does it matter what fixture you use, that the noise occurs?

have you checked your static pressure?
high pressure and quick on/off valves can cause the thumping.

It does not matter what fixture I use. It happens when I use hot water from both shower and sink faucets. Does contracting/ expanding things last for over 2 hours after using hot water? And.. I am not sure if we have plastic drain pipes or not through out the house, but when I open the sink cabinet, black plastic drain pipes are connected to the sink.

Thank you for your reply! I have not check the static pressure, but I hear thump sounds a few minutes after I close hot water faucets, and the thump sounds last about 2 hours with 2-3 minutes intervals. And.. when I open the faucets, water does not bust out of the faucets or gushing out. But do you still it is worth to check the static pressure?



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What you describe is expansion of the ABS Waste pipe inside your walls. When the structure was plumbed, the plumbers did not isolate the pipes from the plates or studs inside your wall and when the pipe is heated up it expands. It is a nuisance and would probably take many years for any damage to the pipe. The fix require opening walls, but you cannot access every area that the friction occurs because it is not accessible.

Thank you for your reply! If opening wall would not help much (I really don't want to open walls) installing circulating pump will solve the noisy problem since the pipes will stay the same size?

The problem is more likely with the drainage piping, not the supply piping, so circulating pump won't help.

Thanks, but what I forgot to mention is that it takes at least a minute or two to get hot water upstairs. Even when I quite do not get hot water from hot water faucets yet (for example, when I wash my hands quickly), I still get thump sounds for a while. In that case, hot water did not drain to the drain pipes. but.. still is it going to be the drain pipes to be blamed for the noises?