just installing a mira realm mixer shower , we have a system boiler with a unvented cylinder . is it best to give the shower a separate 15mm feed pipe for hot water which is branched off the 22mm hot water pipe which goes to our bath ,there is also a 15mm hot water pipe nearby aswell , the 15mm cold supply is already in place from a previous electric shower , this is branched off the main 15mm cold supply that goes to the bathroom . or would it be better to branch off the 22mm cold main that goes direct to the unvented cylinder . .our mains pressure is about 2.5 bar , do we need to fit a pressure regulator for the cold feed into shower .