Electrically powered immersion heating elements and controls therefor

An electric immersion heating element for use in a water boiling vessel, said heating element comprising an elongate resistance heating portion to be immersed in use in water to be heated and an element head portion serving for mounting said heating element in said water boiling vessel, said resistance heating portion comprising an elongate metal sheath within which there is provided a resistance heating wire and said resistance heating wire being electrically insulated from said sheath, said elongate metal sheath having spaced apart ends and said ends being engaged with said element head portion, said resistance heating wire being shorter than said elongate metal sheath so that the resistance heating wire does not extend fully to the ends of the sheath whereby end portions of the sheath adjacent both ends thereof are not directly heated by the resistance heating wire and remain relatively cool in operation, electrical terminal portions extending from the ends of the sheath and, internally of the sheath, extending into contact with the resistance heating wire, a heat transfer element formed of a high thermal conductivity material connected to a directly heated portion of said sheath adjacent to one of said relatively cool end portions thereof and extending through said element head portion to provide for sensing of the temperature of the heating element in use, and an enclosure surrounding said directly heated portion, said enclosure being arranged so that it will fill with water when, in use of the heating element with a water boiling vessel, the vessel is filled, and said enclosure further being arranged so that, when the filled vessel is boiled, the onset of boiling and the consequent generation of steam in the enclosure will cause the water substantially to be expelled therefrom so as to mimic a dry boil situation which can be sensed by an appropriate thermally-responsive control thermally coupled to said heat transfer element.