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Boiler mixer valve issue with cold water at mixer showers

Postby DannyC1986 » Thu Dec 16, 2021 1:23 am

We recently had a plumber come round and install a new mixer valve at the boiler as the previous one had failed causing cold showers and luke warm taps.

Two months later we are having a similar issue however it is only at our two mixer showers which go intermittently warm/cold (never hot).

Water at all of our taps throughout is hot.

I assumed the issue was the mixers on the showers however after investigation the outlet pipe coming from the mixer valve at the boiler goes stone cold when we run either shower but remains hot when we use the taps.

Hot inlet to the mixer valve is at a constant 60 degrees and there is definitely ample hot water in the tank. I have tried the mixer valve from minimum to maximum setting but only get hot water from the taps when close to or on maximum.

Could this be pressure related… eg the hot water pressure isn’t high enough in comparison to the cold so when using a high pressure shower the cold is flooding the mixer valve?

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Simply Build It

Postby stoneyboy » Fri Dec 17, 2021 10:22 pm

Hi dannyc1986,
If you have a mains fed hot water tank, a pressure regulating valve will be fitted on the mains in. If your cold is mains fed without a pressure regulating valve then the imbalance could be the cause of your issues.
Regards S
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