Abstract: A control valve unit for controlling the flow of water through a solar energy system that includes a solar energy heated water storage tank and a conventionally heated water storage tank, the control valve unit incorporating improved valve means which may be installed in a single readily accessible location, which may be easily understood and operated by the users of the solar energy system, and which enables selective independent and/or combined utilization of the separate water storage tanks whereby maximum energy savings may be effected with a minimum of intellectual and physical effort on the part of the users thereof.