This heating cartridge includes a thermally conductive tube (42) to be immersed in a thermo-expandable substance of the thermostatic element, electric heating means (6) arranged inside the tube, and a base (7) made of a plastic substance, integral with a terminal longitudinal portion (44) of the tube and adapted to support the electric connection between the heating means and an external current source. In order to make the connection between the base and the tube both resistant and precisely adaptable to various heating cartridge geometries, and to do so economically, the terminal portion of the tube comprises an outwardly flared free end (45), which extends protruding both radially and axially from the rest of the terminal portion and in which the base is attached by overmolding.