Cooling system for cooling one or more computer servers and for producing heat from heat recovered from the server(s), comprising: - a sealed vessel, filled with a dielectric oil; - at least one electronic circuit board supporting a plurality of electronic components, the electronic circuit board being arranged vertically inside the vessel between a lower portion and an upper portion of the vessel and being immersed in the dielectric oil; - at least one plate comprising a heat pipe, of which the heating zone, called evaporator, is coupled thermally to one or more of the electronic components of one and the same circuit board which are the greatest generators of heat, while the cooling zone, called condenser, is arranged in the upper portion or the lower portion of the vessel, and preferably, an element with developed heat exchange surface fixed onto the condenser; - a water/oil exchanger, arranged outside the vessel; - an oil pump, - a closed fluid circuit, containing the dielectric oil circulated by the oil pump, the closed circuit comprising, in fluidic series: • one of the circuits, called oil circuit, of the exchanger, • a duct linking the oil circuit of the exchanger to the lower portion or the upper portion respectively of the interior of the first vessel, • the interior of the vessel, • at least one duct linking the upper portion or the lower portion of the interior of the vessel to the oil circuit of the exchanger, the closed fluid circuit being thus configured so as to have a series cooling of the components of an electronic circuit board that are the greatest generators of heat, then of the other components of the same electronic circuit board. - a sealed vessel, filled with a dielectric oil; - at least one electronic circuit board supporting a plurality of electronic components, the electronic circuit board being arranged vertically inside the vessel between a lower portion and an upper portion of the vessel and being immersed in the dielectric oil; - at least one plate comprising a heat pipe, of which the heating zone, called evaporator, is coupled thermally to one or more of the electronic components of one and the same circuit board which are the greatest generators of heat, while the cooling zone, called condenser, is arranged in the upper portion or the lower portion of the vessel, and preferably, an element with developed heat exchange surface fixed onto the condenser; - a water/oil exchanger, arranged outside the vessel; - an oil pump, - a closed fluid circuit, containing the dielectric oil circulated by the oil pump, the closed circuit comprising, in fluidic series: • one of the circuits, called oil circuit, of the exchanger, • a duct linking the oil circuit of the exchanger to the lower portion or the upper portion respectively of the interior of the first vessel, • the interior of the vessel, • at least one duct linking the upper portion or the lower portion of the interior of the vessel to the oil circuit of the exchanger, • one of the circuits, called oil circuit, of the exchanger, • a duct linking the oil circuit of the exchanger to the lower portion or the upper portion respectively of the interior of the first vessel, • the interior of the vessel, • at least one duct linking the upper portion or the lower portion of the interior of the vessel to the oil circuit of the exchanger,