The Quooker system consists of a small tank in the kitchen cupboard that is linked to the boiling water tap on the worktop.
The tank acts like a vacuum flask connected to the water mains. The air in the insulated wall is so thin that the heat is unable to escape.
It therefore takes very little energy (just 10 watts) to keep the water in the tank at 108°C. The water only starts to boil when the tap is turned on and the temperature of the outflowing water drops to 100°C. While the water is flowing out of the tap, fresh water immediately flows into the tank.