The original post: /r/diy by /u/BossMafia on 2024-11-10 21:28:14.

Hi all. I’ve been fighting this annoying soft water hammer noise for a little while now. Not quite sure when it started, might have always been here since I bought the house 5 years ago. I marked the TLDR segment below.

There are two sinks in my master bathroom. When opening or closing any of the four taps, I hear three or four light pipe thudding noises. Like instead of the classic metal hammer hitting the pipes sound, it’s more of a soft wooden mallet. Very rhythmic in nature. I installed water hammer arrestors on both supples of one of the sinks, which didn’t change anything.

This past week I changed out the hot water tanks expansion tank and P&T valve after they had both failed. Not at the same time, I think the expansion tank failed a while ago and I just noticed it. After changing the P&T valve the sound went away…until I ran the shower in the master bathroom which led me to figure out that the noise is coming from somewhere in supply lines to the shower mixer.

If I close any combination of isolation valves to the mixer (hot, cold, or both), the hammer completely stops from all four sink taps. I’ve tried restraining the pipes with my hands to see if they’re knocking against any wood in the wall, but nothing I really do there helps much. (I was hoping I could just shim some rubber somewhere if I could find it)

TLDR (Title and… )

I’m assuming the next step is to install some sort of water hammer mitigation on the shower supply lines, after the isolation valves, but to do that I’d have to cut the pipe and I’ve never been great at sweating copper. I see that this exists, but I have three questions:

  1. Would I go to hell for using the sharkbite hammer arrestors?
  2. Are there any other diagnostic steps I could take, or solutions I should look at before going this route?
  3. Given what I mention above about the expansion tank and P&T valve failing, high water pressure comes to mind. But I hooked up a meter, ran a tap and measured a running pressure of ~55 PSI. The house is three storeys, I’m guessing 55 PSI is fine, but could it still be too high?