A flange assembly for holding a heating device to a fluid container of an appliance accommodating a fluid to be heated, in particular a domestic appliance, comprising: a flange unit arranged for being mounted to an opening of the fluid container by at least one fixing unit and having a non-sealing and a sealing and attachment position, wherein the flange unit is reversibly moveable from the non-sealing to the sealing and attachment position by means of the fixing unit for being configured to engage the opening of the fluid container in the sealing and attachment position, wherein the flange unit comprises a sealing element and a tensioning element, wherein the sealing element and the tensioning element are moveable relative to each other in an axial direction by means of the fixing unit such that the sealing element and the tensioning element can be pressed against each other, wherein the sealing element and the tensioning element are, in the sealing and attachment position, arranged to provide a sealing in a sealing direction perpendicular to the axial direction, and wherein the sealing element and the tensioning element of the flange unit comprise each at least one tapered portion (51, 57, 59; 61, 69), characterized in that the at least one tapered portion (61, 69) of the tensioning element overlays over the at least one tapered portion (51, 57, 59) of the sealing element in the axial direction in at least the non-sealing position, wherein the flange unit comprises at least one through opening extending through the sealing element and the tensioning element in the axial direction for receiving and holding an element, such as a heating device or a temperature sensor, and wherein the at least one tapered portion (57, 59) of the sealing element surrounds the through opening and the sealing element is arranged such that, in the sealing and attachment position, the defined displacement of the at least one tapered portion (57, 59) in the sealing direction holds the heating device or the temperature sensor within the through opening. a flange unit arranged for being mounted to an opening of the fluid container by at least one fixing unit and having a non-sealing and a sealing and attachment position, wherein the flange unit is reversibly moveable from the non-sealing to the sealing and attachment position by means of the fixing unit for being configured to engage the opening of the fluid container in the sealing and attachment position, wherein the flange unit comprises a sealing element and a tensioning element, wherein the sealing element and the tensioning element are moveable relative to each other in an axial direction by means of the fixing unit such that the sealing element and the tensioning element can be pressed against each other, wherein the sealing element and the tensioning element are, in the sealing and attachment position, arranged to provide a sealing in a sealing direction perpendicular to the axial direction, and wherein the sealing element and the tensioning element of the flange unit comprise each at least one tapered portion (51, 57, 59; 61, 69), characterized in that the at least one tapered portion (61, 69) of the tensioning element overlays over the at least one tapered portion (51, 57, 59) of the sealing element in the axial direction in at least the non-sealing position, wherein the flange unit comprises at least one through opening extending through the sealing element and the tensioning element in the axial direction for receiving and holding an element, such as a heating device or a temperature sensor, and wherein the at least one tapered portion (57, 59) of the sealing element surrounds the through opening and the sealing element is arranged such that, in the sealing and attachment position, the defined displacement of the at least one tapered portion (57, 59) in the sealing direction holds the heating device or the temperature sensor within the through opening.