Hi

My ensuite shower had very week pressure - cold was just about strong
enough to reach the fixed head, hot was non existent. H&C pressure to
the bath was adequate, but as I wanted to install a tap-mixer shower
here, I decided to have the upstairs pressurised with a pump.

So I’ve just had a Salamander ESP 75 twin impeller pump fitted to
pressurise all hot & cold outlets upstairs. I’ve also fitted the mixer
shower to the bath, which works fine.

However, the ensuite shower, (thermostatic mixer), although it now has
good pressure, it’s output is consistently cold. I’ve checked its hot
supply and it appears to be fine, i.e., isolating its cold supply
outputs hot water at good pressure, albeit way too hot for a shower.

The only I can get an acceptable shower is to simultaneously run the
cold tap on the bath. The ensuite works fine in this situation, the
thermostatic mixer is a joy and responds to the temperature knob as
needed. Ecstasy – it’s just a shame I don’t want to have to run the
cold bath tap every time I shower

My conclusion is that the cold supply to the mixer is at much greater
pressure than the hot. I’m perplexed why as it is fed from the tank,
not from the mains as appears to be a frequent issue from examples
I’ve researched.

I’ve examined the hot & cold pipe work from the pump to the shower and
can’t see anything particularly different - same pipe diameters,
similar length, turns etc.

My questions are thus:-

1. should an impeller pump output equal pressure on hot & cold, in
which case is my shiny new pump not working properly ? Or does it
simply boost input pressures proportionally, i.e., if input hot is
lower than input cold, then output hot will also be lower than output
cold ?

2. Is pressure reducing valve immediately before the cold input to the
ensuite mixer r the way to resolve this ?

Cheers
Gareth.