Apparatus for permissibly heating liquids during the Sabbath comprises a first vessel in which a liquid is received, a heat source for heating the liquid, and cooling apparatus to provide a predetermined regulated liquid temperature. In one embodiment, the apparatus comprises an additional vessel and a reheating vessel, and heating fluid is automatically flowable from the first vessel to the reheating vessel via the additional vessel to heat a liquid at a greater than threshold temperature. The additional vessel has cooling apparatus or an emptying arrangement, or a cooling apparatus is interposed between the additional vessel and the first vessel. In another embodiment, the heat source has a heating element, electrical insulation which is durable within surrounding liquid, and a temperature sensor for detecting heating element temperature or a conductivity sensor for detecting surrounding liquid electrical conductivity. A deactivation signal is transmittable to an electronic adaptor of the heating element.