Why is it that I can only get hot water in my unit block (old building) shower when I have the cold tap in bathroom sink on?

  • 1
    what kind of valve do you have
    – Traveler
    Commented Oct 7, 2023 at 2:20

1 Answer 1


Sounds like you have a mixing valve problem, and opening the cold reduces pressure enough on that side that it no longer dominates what the shower is getting. Either that or there's a restriction (partially closed valve?) In the hot water line which is causing the same effect.

  • Check the lines for a partially closed valve. I would expect a problem on the hot side. Something is causing the pressure in the hot side to drop and opening the cold lowers that enough so things work.
    – Gil
    Commented Oct 7, 2023 at 6:14
  • You can also get this if your cold is mains pressure and your hot gravity fed. The shower part of my bath taps does this (luckily rarely used, as there's a better overhead shower as well) . The solution there is to turn the hot fully on, and then turn on just enough cold to get a reasonable temperature. Opening a nearby cold tap has a similar effect, by diverting cold away from the mixer. Partially closing a valve on the cold would help too, if there was one accessible
    – Chris H
    Commented Oct 7, 2023 at 8:08
  • Thankyou all for your advice. Now I know how to approach the unit block manager.
    – Natasha
    Commented Oct 7, 2023 at 12:25

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