Abstract: A solar heating system comprising a solar collector having its input connected to a pressurized fluid source and its output connected to an input of a fluid storage device, the fluid flow from the output being controlled by a thermally controlled valve, a pressure release valve having one input connected to an input/output near the bottom of the fluid storage device, a second input connected to the pressurized fluid source and an output for discharging the excess fluid, and a pressure reducing valve connected between the pressurized fluid source and another input to the fluid storage device. When the pressure in the storage device increases to a predetermined level the pressure release valve will open and allow the excess fluid to be discharged therefrom. The pressure reducing valve enables the fluid storage device to be replenished if the pressure therein decreases to a level below the pressure of the fluid source.