As is discussed in the article, mains pressure hot water cylinders are more expensive than low pressure ones. Also the installation (ed: of the first mains pre

As is discussed in the article, mains pressure hot water cylinders are more expensive than low pressure ones. Also the installation (ed: of the first mains pressure HWC) is more expensive since it's supposed to be done by a certified plumber where (I'm fairly certain) a homeowner is allowed to replace like-for-like. Anecdotally, it does seem like there is a hesitancy in switching to mains pressure hot water, due to old valves and such failing, but I think the biggest reason is simply that a low pressure hot water system means less heated water going down the drain. From memory, the pipe is just a piece of 1 inch copper. There's nothing on the top, it just points straight up to the sky.