Yes no problem, there's a wide range of boilers available.
Alot of new installations still use 10mm pipework. I'd imagine your's will probably be 8mm pipework.
To use the existing pipework you will need to flush the system a few times (not powerflush, unless you have problems with the radiators or sludge), ideally renew all radiator valves, and check - if not replace the manifolds, as this is where the leaks are likely to occur when changed to a pressurised system.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!