Rational and efficient use of thermal energy in recent years has resulted in significant changes in the heating system as well as technological progress. In order to design a heating system properly and exploit it correctly, an in-depth understanding of the hydraulic issues is necessary. Application of automatic control system in various sectors of heating network has resulted in a more dynamic and efficient work of the whole system. For proper operation of a thermal system it is also necessary to compile a correct heat balance and a regulation graph that allows to determine the optimal mass and parameters of heat medium. The article discusses the problems of supplying heat process, types of thermal systems and selected problems of hydraulic issues that occur in the heating networks.