My son lives in a flat that has 5 rads running off a condensing boiler. The main pipework to the rads is 22mm with with 15mm Ts in to the rads. The pipework is all exposed running around the perimeter walls. We plan to change all this pipework to either 10mm microbore or 15mm rigid and channel out the wall where it meets the floor, to hide this pipework. Would this be in order, or would stepping down to microbore restrict the pressure too much? Some tips also on putting pipes behind the wall would be helpful also please. Many thanks