Abstract: A microprocessor based control system monitors and controls a heat pump water heater system and interfaces the water heating system with an external centralized control system. The microprocessor control system includes sensors, safety switches, device interface relays, user interface devices and precanned software to provide versatile monitoring and control over a heat pump type water heating system. The system generally involves a typical heat pump coupled with a domestic water heater, hot water retention tank or other body of water. The control system provides operational control over the heat pump to maintain the hot water stored in the domestic water heater in a predetermined setpoint and controls the use of electric resistance heating elements in the domestic water heater for added heating capacity for quick heat recovery type operation. The control system receives a centralized signal typically from a utility company to disable heat pump water heating operation during peak demand time periods.