An upright tank (6) stores hot water in layers of ascending temperature for washing, central heating and is draws its power from sources with varying output e.g. solar panel or heat pump. The tank has a central upright water distribution cylinder (7, 11) with water apertures (12) at different heights. The cylinder (7, 11) is mounted on a lower cylinder (8) holding the heating element (15). Hot water rises by convection from the element (15) to the appropriate level where it is discharged through the appropriate aperture (12).
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