A heat exchanger (10) for arrangement inside a service-liquid tank (12), in particular inside a motor-vehicle service-liquid tank (12), comprising: a heat-exchanger liquid reservoir (14) for receiving a supply of liquid (22), an electric heating device (20) which is constructed and arranged for the transfer of heat into the heat-exchanger liquid reservoir (14), and a heat-exchanger line (24) which originates at least from the heat-exchanger liquid reservoir (14) and which is designed for the transfer of heat from the liquid flowing in the heat-exchanger line (24) to an area (26) outside the heat-exchanger line (24), characterized in that the heat-exchanger line (24), as a circulation line, discharges into the heat-exchanger liquid reservoir (14).