Current mains pressure and flow rate is 1.5 bar and 16 ltr/p min. respectively. I need to increase the flow rate to at least 20 ltr/p min. as a basic requirement for installing an unvented hot water system (megaflo). Before outlaying the expenditure for doing this, can someone who has done it tell me whether replacing the existing lead pipe from the outside mains into the property with say a 25mm or 28mm blue pipe might give me the extra flow that I need? The rest of the pipework in the property is 22mm (except those that tee off to the sink and garden taps are 15mm).