horizontal cylindrical conduit 19 bounded by two seal rings 20 and 21 of o ring type the ball 18 is arranged to be urged against the seal ring 21 to close an outer hole 22 or be urged against the opposite seal ring 20 to close an inner hole 23 by even a light flow of an aeriform substance said aeriform substance can be either environmental air or the air expanding within the boiler following activation of the armoured resistance element 7 when it begins to heat the water the facility for closing either the outer hole 22 or the inner hole 23 enables this valve to perform the important function of drawing air into the boiler 5 when the boiler has completely cooled after the apparatus has been used in this respect in this state there is the tendency inside usual boilers for a vacuum to be created if said boilers are of the type fed by micro pumps there is the drawback that they restore atmospheric within their interior by drawing water from the reservoir via passage through the pump body hence a water level arises within the boiler which is higher than that required for correct operation on next activating the boiler this level determines delayed heating with initial spitting of water instead of only steam emission with the floating valve of fig5 this drawback is eliminated by the said drawing of air in a direction 24 which detaches the ball 18 from the seal ring 21 but without having sufficient energy to urge it to effectively bear against the seal ring 20 sufficient energy is however possessed by a contrary flow 25 generated by the activation of the armoured resistance element 7 in this respect this resistance element provides a heating.