I have a 25mm cold water mains coming into my house under the sink downstairs. Then a 15mm stopcock followed by a 15mm pipe going to a Valliant 35w combi boiler. On the way to the boiler this pipe T’s off to the downstairs sink, dishwasher, then upstairs to the toilet, basin, bath and then finally the thermostatic shower valves before feeding the boiler. A 15mm hot pipe then comes from the boiler and T’s off with 15mm pipes to the thermostatic shower vale, bath, basin, then lastly the downstairs sink. I am renovating the whole house so my question is this. Should I replace the 15mm pipe feeding my boiler with a 22mm with 15mm T’ing off to the appliances? And is it also worth replace the 15mm hot pipe coming from the boiler with a 22mm with 15mm Ting off to the appliances? I can draw a diagram if my explanation is not enough. I am also thinking of adding a three zone underfloor heating at a later date.