Shower Problem

I have a couple of headaches one i fitted a salamander whole house shower pump the noise sounds like my preesure washer.Secondly i am pumping just my hot water supply round the house along with hot and cold to the shower after i turn the shower off then a couple of minutes turn it on i have no water from the shower it seems to be draining back.any ideas?

Non return valves on the shower supplies

Cheers Lee
It says in the manual do not use non return valves