Unless your hot water storage tank is designed to be pressurised (and that's unlikely if you have a low pressure system as the unvented cylinders are more money) then it will need to replaced. You will also need to fit other items such as a expansion vessel as well as safety and various pressure controls.
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!