PURPOSE: To prevent water cooled at night from flowing back into a hot water storing tank of a solar water heater, by forcibly circulating water contained in the tank through an inverted U shaped pipe provided between the tank and a heat-insulating material and a heat-transmitting medium passage provided on heat-collecting plates so that the heat of the plates is efficiently transferred into the tank.

CONSTITUTION: A solar heat water heater is provided with the hot water storing tank 15 located below the heat-collecting plates 12 provided on the heat-insulating material 13, and water in the tank 15 is forcibly circulated by a circulating pump 19 through the inverted U shaped pipe provided between the tank 15 and the insulating material 13 and the heat-transmitting medium passage 14 provided on the plates 12. When the temperature of the plates 12 is raised, the pump 19 is operated by the temperature difference between a temperature sensor 21 and a temperature sensor 22, water in the tank 15 is circulated through the passage 14, and heat is transferred from the plates 12 into the tank 15. Since the tank 15 is thermally insulated by heat-insulating materials 13, 20, heat is sufficiently insulated. Even when the temperature of the plates 12 is lowered at night, a temperature gradient in the temperature of water in the pipe 18 prevents water cooled in the plates 12 from flowing back into the tank 15.