I have a problem after on just fills a bath only 1/3 , in that there is then no hot water ! I have a typical CH system ie gravity fed ect , A potterton netaheat 10/16 boiler. The Cylinder size is approx 400mm wide by about 1 metre high. Is it the fact that the cylinder capacity is too samll for a 4 bed house ? Could i fit a larger cylinder bearing i n mind that 400 mm diamater is most that is feasable but could go higher in height . Also preasure for hot water is not good when having a shower esp two persons runnig it . The head of tank is only about 3feet above cylinder. what practical alternatives do I have please ?