Hi, looking to change a couple of pipes for plastic pipes, the hot copper pipe is not a problem, the cold water pipe is a old steel pioe that runs under floor and inside wall through bedroom and bathroom, trying to kill 2 birds with one stone as the old steel pipe is in the wrong place in the bathroom and I want to replace it, as iam in the process of gutting the kitchen I need to get these pipes changed and some electrics moved so I get my plasterer in and this is holding me up I would like to bury the plastic pipes in wall??? Any suggestions, will try to add pics tge steel pipe is thicker possibly 22mm?? Would it make any difference upstairs if it was changed 2 15mm ?