Hello all. I was wondering if you maybe be able to help. I currently have an old system that I'm just about to replace. The flow and return pipes are naturally 22mm and at the split valve where it T's off these reduce to 15mm to heat the hot water cylinder. I have a Worcester 30CDi system boiler to go in and was wondering if it's ok to keep these 15mm pipes to the cylinder or if they really must be increased to 22mm (involves digging up the floorboards which isn't fun !).  Was also curious as to what size the pipe is inside the cylinder as well.
Many thanks in avance for any advice

Lee