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With the shower on, I hear a thumping noise behind the wall and the water pressure immediately drops. This happens every few days, so not every time I take a shower. It happens almost immediately after I pull up on the lever to transfer the water flow from the tub spigot to the shower head. Sometimes, if I turn the shower off, push down the switch to drain everything through the tub spigot, and wait for one minute, I can turn the shower back on and the pressure is back up. This doesn't always work, though.

The pressure, once dropped, will remain the same through both hot and cold temperatures. The only recent work done in the house was the replacement of the air conditioner unit and the replacement of my expansion tank above the water heater. The sprinklers are not usually on during the time I take a shower.

I have been unable to find any sort of leak or water stain anywhere. The noise, which I would describe as halfway between a clunk and a thump, with a dash of bump thrown in for good measure, sounds like it is coming from behind the shower, between the tub spigot and the shower head. My unit is a combination bath/shower, if that matters.

Any ideas or suggestions? Any other information I can offer? The last thing I feel like doing is plumbing work, but if there's a serious problem coming my way I'd like a heads-up and a chance to fix it before it makes a mess.

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    Great description of the sound! Have you tried taking the shower head off and running the shower, to see if anything other than water comes out. Could be some junk knocked loose during the expansion tank replacement, traveled up the line to the shower.
    – Tester101
    Commented Jul 2, 2014 at 14:02
  • @Tester101, thanks for the suggestion. I will try that tonight and let you know :)
    – AHiggins
    Commented Jul 2, 2014 at 14:44
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    I tried running the shower without the showerhead a number of times but nothing ever came out. The problem seems to have gone away on its own, though, since I haven't heard the sound or experienced the drop in pressure.
    – AHiggins
    Commented Jul 10, 2014 at 16:06

2 Answers 2

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Could be a clump of solder is in the pipe. I had the same problem recently and ran the shower for a while without the shower head. I never found anything but the problem went away. Maybe it was a glob of flux that finally dissolved.

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The thump is probably coming from the pressure balancer. This is designed to stop you getting scalded if someone flushes the toilet, or frozen if someone runs the hot tap. If either happens it will lower the pressure to balance the hot and cold.

Assuming nobody has done either, then you may have a damaged o-ring in the balancer. There are lots of different shower valves, but if you google it you'll find out where it is. It usually is a big-old screw or nut on one of the inlets close to the mixer. Google replacing the pressure balancer, but its typically the o-rings than can get sheared, can cause sticking and thumpy triggering. Good luck.

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