Apparatus for producing hot water; apparatus for the supply of hot water; boilers for hot water supply installations; electrically heated hot water tanks; gas fired boilers for producing domestic hot water; hot water apparatus; hot water boilers; hot water boilers for beverage making; hot water bottles; hot water cylinders; hot water heaters; hot water heating installations; hot water installations; hot water supply heaters; installations combining boilers and steam generators for producing hot water; radiators for hot water installations; radiators for hot water systems; safety apparatus for controlling the distribution of fluid in hot water installations; evacuated heat pipe solar collectors (heat exchangers); solar collectors (heating); solar collectors (lighting); solar collectors for heating; solar energy collectors for heating; solar energy powered heating apparatus; solar energy powered heating installations; solar furnaces; solar heating apparatus; solar heating installations; solar heating panels; solar lamp units; solar lamps; solar panels for use in heating; solar powered ventilation apparatus; supports adapted for use with solar heating tubes; thermal storage apparatus (solar energy) for heating; thermal storage instruments (solar energy) for heating