<p>This research work is aimed at ensuring the improvement of energy efficiency and reliability of self-directed solar heating by optimizing the hydrodynamic modes of operation. Proceeding from this purpose, the tasks of the research are to analyze existing methods of protecting solar collectors of water heating and hot water supply systems from freezing and to reveal the most perspective methods. One of the tasks is also to determine the laws of hydrodynamics in self-draining of solar heat supply.</p>