Thermostatic Mixer Shower - Pressure of cold water?

[martinini]

Hi
I have recently had a Bristan thermostatic mixer shower installed over the bath but it doesn't seem to be working properly.
At certain times of the day ie 6am the shower is luke warm yet at 6/7pm it is hot. Also if turn the cold tap on in the bath the shower gets hotter. I have had a comedy plumber out to this about 5 times and asked the question, Is it something to do with cold water pressure being too high and outweighing the hot water entering the shower? But he has given no solution to the problem.
The shower runs from an Worcester bosch oil combi boiler.

Would fitting a pressure isolating valve to the cold water pipe that leads to the shower do any good ?
As you can tell I know nothing about showers/plumbing etc.
Any advice would be great

 

[dhutch]

Its not a large an effect as that. But I notice the temperature of my combi powered mixer shower (main 30he) drops of if I shower late at night (like 1am) compaired to at half 7 in the morning.

I put it down to increased mains pressure, and find turning the flow down to just below flat out raises the temp back to where it was at only a small reduction in flow rate.


Daniel

 

[Charnwood]

Presumably neither of you have thermostatic shower mixers.
Thermostatic showers regulate the temperature to +/-2°C from the set temperature. This would not be noticeable.

 

[dhutch]

Minds also thermostatic, an aqualisa midas 200 bsm to be exact, and it works fine. Until such time as there is enough flow to pull the boilers output down below the desired temp, at which point, it fails to maintain temp. This is my reading of the situation anyway.


Daniel

 

[Charnwood]

Your last paragraph; mains pressure changes would affect both hot and cold.

 

[dhutch]

Your last paragraph; mains pressure changes would affect both hot and cold.

Yes, but if the flow through hot (and cold) increses to a point where the flow through the boiler means the output temp begins to fall, the valve can only compenstate as far as taking 100% of the water from the hot feed, and if this then falls below the desired temp, the shower temp will fall. Unless the mixer is clever enough to throtall the output due to the hot feed being too cold, which as far as im aware they do not do.

Although they will in effect throtal the output if the cold feed fails to provide enough to kept the temp from excedding the the desired output, they do not do the reverse if its getting to cold. How would they know if its of a combin and that it would help.

Might be wrong, buts that what I see.

 

[martinini]

Presumably neither of you have thermostatic shower mixers.
Thermostatic showers regulate the temperature to +/-2°C from the set temperature. This would not be noticeable.

It does say Thermostatic mixer shower on the website, the box and the instruction booklet but maybe you are right - who knows?

Thanks for the help