Hot water supply system

Hot water supply system 800 comprising an insulated 804 thermal energy store 806 for storing energy from a heat pump, and a supplementary heater 820 to supply a hot water outlet 810 from the store. A valve 818/822 controls flow of water to the energy store and/or supplementary heater. A controller 830, in response to a control input which includes a desired flow rate, determines a normal drive signal to control the valve to meet the desired flowrate and the controller applies an initial drive signal of higher magnitude for an initial duration, followed by the normal drive signal in order to reach the desired flowrate instantaneously. The control input may be a signal from a flowrate sensor incorporated into the valve and may terminate the initial duration in response to information received therefrom. The control input may also be temperature sensor data. The controller may store relationship data between the normal drive signal and an indication of flowrate to determine normal drive signal. There may also be a second valve controlled based on the control input. A predetermined algorithm may define alternate use of the two valves for different time periods. The thermal store may contain phase change material.