The invention relates to a thermo heater comprising: a glass store (1) provided with a lid (7), and magnetrons (3) supported by a belt or supporting frame (2) surrounding the store (1), allowing the continuous support of the magnetrons and the arrangement thereof inside the store (1), each magnetron being received on a primary exchanger (5) which is, in turn, received on a main exchanger (6). A solenoid (8), a rod thermostat support, and the water inlets and outlets are arranged on the lid, and a mixing valve (20) is arranged below the lid, said mixing valve being connected to the lid by means of a controller (17) and actuated by means of a piston (15) connected to the solenoid. The mixing valve is a double-filter valve. The characteristics of the materials used enable almost instantaneous heating, a reduction in energy consumption, and effective protection against the proliferation of colonies such as legionella.