A dishwasher and associated control method are provided wherein a water supply manifold supplies a wash chamber with wash liquid. The supply manifold includes a hot water inlet from an external hot water source and a separate inlet from a storage tank, and is configured to be selectively actuated between the hot water inlet or storage tank inlet. A controller is in communication with the supply manifold and is configured to act on a signal that is indicative of an actual or pre-defined high electricity demand period on a power supply to the hot water source. The controller is configured to generate an output control signal to the supply manifold to cause the manifold to direct substantially only water from the storage tank to the wash chamber during the high electricity demand period.