Abstract: A solar water heating system having main solar panels for collecting heat from the sun and transferring the heat to water flowing through it from an inlet line to a storage tank. A control system is located to shut the flow of water and drain the system when the absorbed radiation by the panels is below a predetermined level and to commence the flow of water and shut the drain when the radiation level is above the predetermined level. The control includes a conduit for transferring heat from a main panel or an auxillary panel to a thermostat which acts to move a lever. The lever thereafter controls the opening and closing of a drain valve and an inlet water valve either directly or through other levers and connectors.