thermostatic power shower

4 Jan 2007
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United Kingdom
I have recently installed a power shower with a stuart turner pump ST55. In the shower itself I have a thermostatic mixer from which the shower head is connected. There are different settings on the mixer but I have mine set for 38 degrees. The problem that I am having is that the hot water is not staying at that temperature for the duration of the shower. The temperature decreases and I find that I have to adjust the setting during the shower to increase the temp. Any advice would be great!
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Which valve??? The shower fittings i.e. pump, warix flange, piping, mixer are all new and shower has been installed a month. I am using the emersion in the hot water cylinder for the hot water. As a side note I have two domestic sized hot water cylinders piped in "series" in the hot press. Cold feed comes from tank in attic to bottom of cylinder A. Then goes out the top of A into the bottom of cylinder B. Hot water comes out top of cylinder B where the warix flange is fitted. I only have an immersion heater fitted in cylinder B. I am thinking of fitting a second immersion heater into cylinder A as maybe there is not enough hot water available for the shower??? Confused I know I am.
Brenny, Softus was asking what the model of the actual thermostatic valve was.
Did you commission the unit as per mi, as usually you can adjust the unit to provide the the correct and stable temperature.

A power shower by nature does as it says and uses up alot of h/w so it maybe that you have not enough on tap.
Does the water get hotter if you increase the setting after it starts to get cooler?
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Most pump manufacturers give a maximum temp for the hot water (about 60 deg C) which if exceeded can cause the hot water flow to fluctuate. (I think it causes cavitation in the pump)

I find what you describe happens with my powershower if I heat the water with the immersion heater (which is very hot even on the lowest setting), but it works fine when heated by the boiler because the cylinder thermostat and hence the water temperature is lower.
Pete sorry bout that, I am using a Unichrome NENE thermostatic bar mixer shower from Triton and I am happy with the installation. The temp. does get hotter after I increase the setting but goes cooler again quiet quickly. As you say I might not have enough h/w on tap.

Stem, I have my immersion set for 60 deg. so I would be happy that the h/w temp. leaving the cylinder would be right. I have installed a geothermal heat pump as my heat source for the house which has underfloor heating upstairs and downstairs. I am using this heating which is approx 35 deg. through the coils in the tank which are piped in series through both cylinders. Therefore the temp. from that would not be sufficient for the power shower unlike your boiler. I use the immersion to take the temp. up from 35 deg. to 60 deg.

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