Refilling device for a hydronic heating system, having a monolithic housing providing an inlet port, an outlet port, a middle section providing a flow channel for water extending between the inlet port and the outlet port and a connection socket for a softening and/or demineralization cartridge, wherein the refilling device is connectable to a water supply pipe of a water supply system through said inlet port, wherein the refilling device is connectable to a water supply pipe of a hydronic heating system through said outlet port, an inlet shut-off-valve at least partially accommodated within said monolithic housing downstream of said inlet port, an automatically actuated outlet shut-off-valve at least partially accommodated within said monolithic housing upstream of said outlet port, a system separator having backflow preventers (30, 31) at least partially accommodated within said monolithic housing, a conductivity or TDS sensor (32, 33) at least partially accommodated within said monolithic housing, a flow meter at least partially accommodated within said monolithic housing, a softening and/or demineralization cartridge connected to said connection socket, wherein the softening and/or demineralization cartridge has a RFID or NFC tag storing data about the softening and/or demineralization cartridge, a controller mounted to said monolithic housing, wherein the controller is configured to receive signals from the conductivity or TDS sensor (32, 33) and from the flow meter and receives data from said RFID or NFC tag, wherein the controller is configured to process said signals received from said sensors (32, 33, 35) and said data received from said RFID or NFC tag to automatically control the operation of the refilling device. a monolithic housing providing an inlet port, an outlet port, a middle section providing a flow channel for water extending between the inlet port and the outlet port and a connection socket for a softening and/or demineralization cartridge, wherein the refilling device is connectable to a water supply pipe of a water supply system through said inlet port, wherein the refilling device is connectable to a water supply pipe of a hydronic heating system through said outlet port, an inlet shut-off-valve at least partially accommodated within said monolithic housing downstream of said inlet port, wherein the refilling device is connectable to a water supply pipe of a water supply system through said inlet port, wherein the refilling device is connectable to a water supply pipe of a hydronic heating system through said outlet port, an inlet shut-off-valve at least partially accommodated within said monolithic housing downstream of said inlet port, an automatically actuated outlet shut-off-valve at least partially accommodated within said monolithic housing upstream of said outlet port, a system separator having backflow preventers (30, 31) at least partially accommodated within said monolithic housing, a conductivity or TDS sensor (32, 33) at least partially accommodated within said monolithic housing, a flow meter at least partially accommodated within said monolithic housing, a softening and/or demineralization cartridge connected to said connection socket, wherein the softening and/or demineralization cartridge has a RFID or NFC tag storing data about the softening and/or demineralization cartridge, a controller mounted to said monolithic housing, wherein the controller is configured to receive signals from the conductivity or TDS sensor (32, 33) and from the flow meter and receives data from said RFID or NFC tag, wherein the controller is configured to process said signals received from said sensors (32, 33, 35) and said data received from said RFID or NFC tag to automatically control the operation of the refilling device. wherein the controller is configured to receive signals from the conductivity or TDS sensor (32, 33) and from the flow meter and receives data from said RFID or NFC tag, wherein the controller is configured to process said signals received from said sensors (32, 33, 35) and said data received from said RFID or NFC tag to automatically control the operation of the refilling device.