Thermosatic Mixer Shower - Temperature hot & cold

Hi,

I have just installed a thermostatic mixer shower in my bathroom and have a problem where it cycles hot then cold then hot again. I have a combi boiler and the pressure at the boiler is 1.4 and on watching the boiler when the shower runs the boiler keeps turning on then off then on.

I have replaced the shower mixer with another one as I thought the first was faulty but the second is giving the same problem.

Is it that i have a problem with the water pressure and need to install a pump or is there something else i need to do as 2 different thermostatic mixers are doing the same thing. The water temperature out of the sink and bathroom basin taps are spot on and it only appears to be the shower that is playing up.

Any help as to what may be wrong would be appreciated as at the moment i am of the opinion that i have wasted a fair bit of money on a shower mixer that is useless.

Tearing my hair outin need of help
boxecutor

Quite unusual for this to happen on a combi. The pressure of 1.4 on the boiler is for the central heating and has no bearing on the hot water flow.

The only thing that springs to mind is that the cold is backflowing into the hot, thus causing the combi to turn off (since at that moment the hot is not being drawn from it). One solution may be to install double check valves on the supply pipes.

Well have managed after some agro and lots of surfing the net to discover what the problem was.

The temperature of the hot water from the boiler was too high and so have wound it down which has solved the problem and the shower now works fine.

Obviously this has reduced the water temperature to the sink and basin taps but this is not a major amount that would cause any problems.

Many thanks to all those who have looked at this and to the replies.

Boxecutor