Valve controller in combination with an energy harvester

A valve controller 1 controls a flow of fluid through a valve and an energy harvester 3 harvests energy from the fluid. The valve controller includes an energy store that receives the harvested energy. When the amount of energy stored by the energy store falls below a predetermined level, the valve controller opens the valve to enable fluid flow. Preferably, the valve controller is an electronic thermostatic radiator valve (eTRV) and the energy store is a capacitor. The eTRV can be used in a building heating system whereby thermal energy of hot water passing through a pipe feeding the eTRV is used to generate electricity using the Seebeck effect to be stored in the capacitor. The eTRV may be operated in a fully operational, partial power-down or powered-down configuration. The eTRV may be wirelessly linked with a central control unit 17 so that the eTRV can communicate its configuration to the unit. Ensuring that the valve is opened when the amount of energy stored falls below a predetermined level ensures that the eTRV can be recharged in the event of total power loss by harvesting energy from hot water passing through the valve.