A professional coffee machine includes a supporting frame; a boiler mounted thereon with a tank of at least 8 liters receiving water and heating it to a temperature of about 122-130° C. for the thermo-controlled production of pressurized steam; a preheater having a first heat exchanger associated to the boiler so that the boiler water heats, by heat exchange, the supply water crossing the first exchanger to a first temperature T1 that is lowerly close or substantially equal to a second temperature T2, optimal for preparing a coffee infusion; a dispensing unit of the coffee infusion having its own thermo-controlled heating element, configured to bring the water outlet from the preheater to the second temperature T2, if T1 is less than T2; a thermal insulating member that mechanically constrains the dispensing unit to the supporting frame; and a dispenser of pressurized steam in communication with the tank.