Help with mixer shower install

[EasterEEL]

My plumber is fitting a mixer shower and has supplied it with mains pressure water approx 2.0bar and gravity drop hot water pump assisted to 1.5bars. The problem is when using the shower the hot water pump comes on but cuts out when using the mixer to get lower temp water. Once this happens it necessary to turn the shower off and start again from hot (to get the pump started again). He is adamant this should work and the problem is with the mixer shower (it cost over £100) and wants me to buy a different mixer shower.

I think he should have used a twin pump and gravity fed it with hot and cold to supply hot and cold to mixer shower.

Please can you advise.

 

[E4gas]

Sounds like unequal pressure , you was right in thinking about twin pump for the mixer

 

[PlumbBobBob]

unequal pressure like this wont work the cold is pushing back up the hot and overpowering the pump. one way to get round this would be to fit a non return valve on the hot feed to the shower.

 

[EasterEEL]

Thanks for the quick responses. To clarify the pump is a Salamander CT55 single which turns on and pumps hot water when the shower mixer tap is opened. Is there be a chance that fitting a non return valve would allow this pump to continue working when the mixer tap is moved to mix water to lower temp without cutting out?

 

[PlumbBobBob]

yes, what it is is a valve that only lets water flow one way so hot can flow from the pump but cold from the shower valve will be stopped. designed for this application