Hello all im installing a new bath etc in my bathroom and the mixer valve does both the bath and the shower. The connections onto the mixer are 22mm. Cold water is from the mains (good pressure) and the hot water is from combi. All current pipe in the bathroom including the current bath feeds are 15mm. Can I run 15mm hot and cold to the mixer then step up to 22mm for the mixer connection? I know the bath will fill slower on 15mm than 22mm but are there any reasons why this will not work?