Heating system and thermal energy store

A hot water system 100 comprises at least one heat source, a tank 110 providing an energy source, and a fresh water station 152 provided by a heat exchanger 154 fuelled by the tank. The energy source includes a phase change material (PCM) 170. Most preferably, the tank is a hot water cylinder wherein the PCM is located in an upper part 114 of the tank and the at least one heat source comprises a ground or air source heat pump 133, a solar collector 132 and solar photovoltaic panels 131. Water in the upper part of the tank may be at a higher temperature than water in the lower part so as to provide a stratified thermal energy source. The PCM can be a salt hydrate such as sodium acetate trihydrate that is provided packaged in a plurality of plastic pouches supported on one or more sheets, the vertical extent of the pouches being limited to prevent segregation of the salt within through convection. In use, thermal energy stored in the PCM is used to heat water of the tank passed to the heat exchanger, which is used to heat fresh water for domestic hot water purposes.