shower pump

Hello. I'm fitting a shower and bath (shower in the bath) and while things work ok(ish) I have a bit of a pressure problem. The cold is fed from the mains in a 15mm pipe and is just fine (although I had to feed it into 22mm to fit the taps & shower valve). The hot comes via a 22mm pipe and while adequate could do with some extra pressure. The shower valve (thermostat) is designed to work with a mixture of gravity and mains. Now I have plenty of space for a shower pump but I can only find pumps that feed both supplies. I don't want to pump the cold (I think it's illegal anyway), just pump the hot. Does any one know of a supplyer of a single feed pump (with built in flow switch etc) or can you advise if it's ok to use a two feed pump (about 1.5 ~ 2 bar) but leave one side unused.

I should think all shower pump manufacturers would do a single version - certainly Techflow do (I've got a couple spare!).

the hot and cold supplies to the pump should be of equal pressures, if you are using cold main to the valve and gravity pumped hot via the pump then you will have problems mixing in the valve, hth.