I just had my water heater replaced (by a professional) and everything is great except the bathtub fixtures (shower head and tub faucet) in just one bathroom. The water pressure is really low, especially when it's turned to hot. Every other fixture in the house works fine (even upstairs).

I took off the tub faucet fixture to see if sediment had accumulated in there, but when I turn on the water and watch it come straight out the piping, I see the same thing. Decent pressure if it's on cold and slows to a trickle when turned all the way to hot.

I'm getting the run-around from the installer and don't want to call a plumber if I can fix this myself. I can see almost the entire run from the heater to the tub, which is all copper piping, and I have access via a wall panel to the fixture from behind the tub.

  • unfortunately "professional" and "competent" are not always the same. If they did any soldering, this: diy.stackexchange.com/questions/48785/…
    – Ecnerwal
    Nov 11, 2014 at 22:58
  • ...making the assumption that it worked fine before the heater was replaced and does not work now, anyway. If it didn't work before, could be the same issue but someone else's soldering job, or what @longneck suggests.
    – Ecnerwal
    Nov 12, 2014 at 3:07

1 Answer 1


Sounds like you need to replace the mixing valve. This is a simple part to replace. This usually involves removing the handle and possibly the trim, then removing a retaining clip, and the pulling out the cartridge. Buy a new one and reverse the process.

Here's a good set of instructions for Moen valves: http://www.moen.com/consumer-support/installation-help/tutorial?id=moen0133

  • Thanks! I took apart the mixing assembly and it turned out there were bits of solder stuck in one of the pressure regulator pistons. After removing it, everything is back to normal.
    – Paul D
    Nov 12, 2014 at 19:37

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