can anyone help me i have an old square water heater tank it has three pipes one feeding it with a ball valve one to my hot tap and an overflow pipe it has started leaking and needs replacing i live in a flat and cant see a water storage tank anywhere so i presume that it is an unvented system would i be correct in thinking this or am i talking crap i cant find a tank similar and want to know how to replace it any help would be greatly appreciated