I've installed a thermostatic mixer into my shower; unfortunately now when I raise the shower head height to above my head (or any useful height really) the water comes out cold. If I keep the shower head very (unusably) low it operates as it should.

The hot pipe feels very hot as it should so I'm not sure why it's not allowing hot water through the mixer?

I have a very old hot water cylinder in my house, the pressure is not the best but it's also not that bad considering. Its located on the same (single) floor of the house. The previous shower mixer pressure was adequate but getting a decent temp was frustrating.

rough install

  • 1
    What do you mean when you say "getting a decent temp was frustrating" when talking about the old setup? I am going to guess that your problem has nothing to do with your mixing valve but rather you have a pressure or supply problem with your hot water.
    – jwh20
    Oct 3 '20 at 12:01
  • I mean the shower was either too hot or too cold & the temp would bounce around when adjusting the handle
    – boomshanka
    Oct 3 '20 at 16:26

The height of the cylinder is immaterial. Is the hot water from a loft tank or the mains pressure supply?

In most cases the hot and cold must be from the same supply or at the same pressure for a mixing valve to operate successfully. You can boost the hot with a pump or raise the height of the header tank, use a pressure reducing valve on the cold to reduce it to closer to the hot, or use a mixing valve which will tolerate differing supply pressures.

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