Backflow-heating-filter, comprising (a) a closed housing (18, 20; 218) adapted to be integrated into a heating circuit, the housing having an inlet (14; 214) and an outlet (16; 216) each of which being connected to the heating circuit and a closable drain (26; 226); (b) an essentially cylindric filter sleeve (42; 242) arranged inside the housing, the filter sleeve having a diameter which is selected such that an intermediate space (46, 246) is formed between the filter sleeve and the housing which is connected to the inlet, and (c) filter material (58; 258) inside the filter sleeve (42; 242) for removing particles from the water flow flowing in an operating state through the heating circuit and from the inlet through the intermediate space and via a transition through the filter material of the heating filter, (d) wherein the filter sleeve or a lifting element provided inside the filter sleeve is moveable in an axial direction between two stops (50, 54; 263, 262) and which can be moved from an operating state to a backflow state; characterized in that (e) the transition (56; 256) from the intermediate space (46; 246) to the inside of the sleeve (42; 242) is blocked in the backflow state; (f) the filter material (58; 258) is formed by granulate, balls or other swirlable material having a density which is smaller than the density of water whereby the material will swim at the water surface,, (g) the housing is provided with a fresh water inlet (118; 318) for fresh water from a fresh water supply, and (h) the connection from the fresh water supply to the heating circuit is interupted in the backflow state while fresh water from the fresh water supply can be flowed through the filter material to the drain in a direction opposite to the direction of the water flow in the operating state. (a) a closed housing (18, 20; 218) adapted to be integrated into a heating circuit, the housing having an inlet (14; 214) and an outlet (16; 216) each of which being connected to the heating circuit and a closable drain (26; 226); (b) an essentially cylindric filter sleeve (42; 242) arranged inside the housing, the filter sleeve having a diameter which is selected such that an intermediate space (46, 246) is formed between the filter sleeve and the housing which is connected to the inlet, and (c) filter material (58; 258) inside the filter sleeve (42; 242) for removing particles from the water flow flowing in an operating state through the heating circuit and from the inlet through the intermediate space and via a transition through the filter material of the heating filter, (d) wherein the filter sleeve or a lifting element provided inside the filter sleeve is moveable in an axial direction between two stops (50, 54; 263, 262) and which can be moved from an operating state to a backflow state; (e) the transition (56; 256) from the intermediate space (46; 246) to the inside of the sleeve (42; 242) is blocked in the backflow state; (f) the filter material (58; 258) is formed by granulate, balls or other swirlable material having a density which is smaller than the density of water whereby the material will swim at the water surface,, (g) the housing is provided with a fresh water inlet (118; 318) for fresh water from a fresh water supply, and (h) the connection from the fresh water supply to the heating circuit is interupted in the backflow state while fresh water from the fresh water supply can be flowed through the filter material to the drain in a direction opposite to the direction of the water flow in the operating state.