A heat insulating facility(16) in the form of an air gap is located on the side of the heating device(15) opposite the fluid outlet element(13). The heating device has a protrusion(20) which engages with the inner face of the body element(11) of the wash nozzle. The fluid channel(12) may consist of a main passage(12b) located on the upstream side, and a number of branches(12a) connected to the main channel. The heating element is located between the branches.
