Abstract: In a preferred embodiment, a liquid level sensor for use in a hot, pressurized liquid, including: an outer housing suitable for immersion in the liquid; an inner housing disposed within the outer housing and containing therein electronic/electrical components; detection apparatus disposed within the outer housing and the inner housing to detect level of the liquid; a space defined between the outer housing and the inner housing; and means to permit the liquid which migrates through a wall of the outer housing into the space and which is vaporized therein to pass to the ambient surroundings, so as to preclude migration of the liquid through a wall of the inner housing.