NOVELTY - The boiler (1) includes a first chamber (2), a second chamber (3), and a heat exchange region (4) which can be connected to the first and second chambers and which is provided with a water heater (5) connected to a heat source. The first chamber is arranged at a higher level than the heat exchange region to allow water circulation by natural convection between the first chamber and heat exchange region. A forced circulation unit (6) is provided for forced circulation of the water between the second chamber and heat exchange region.    USE - Boiler for solar panel systems. Can be used in systems for generating heat energy by means of solar panels.    ADVANTAGE - Provides a boiler which is capable of ensuring optimum temperature stratification and of performing a rapid heating of the water meant for hydraulic and sanitary systems in any condition of supply of heat energy to the water to be heated. Ensures that the boiler which, thanks to its particular constructive characteristics, is capable of giving the greatest assurances of reliability and safety during its operation. Ensures that the boiler can be obtained by means of commonly commercially available components s and materials so as to be competitive also from a merely economical standpoint. Allows to achieve optimum stratification of the temperatures inside it, differently from traditional boilers, with which, for an equal heat energy transferred to the water in the boiler, it is possible to achieve at best a uniform temperature of the water in all the boiler of approximately 46 degrees Celsius, which is insufficient for generating sanitary water, i.e., water for user devices such as a shower. Allows to heat the water by means of a natural circulation in a smaller volume of water than boilers of the background art with a tank of equal capacity.    DETAILED DESCRIPTION - The first chamber is designed to contain hot water. The second chamber is designed to contain water at a lower temperature than the water contained in the first chamber. The first chamber, second chamber and heat exchange region are defined axially within a single tank (7) which has a cylindrical shape with a vertical axis.    DESCRIPTION OF DRAWING(S) - The drawing is a top perspective view of the boiler shown partially in phantom lines.    Boiler (1)    First chamber (2)    Second chamber (3)    Heat exchange region (4)    Water heater (5)    Forced circulation unit (6)    Tank (7)