Energy supply device comprising a supply means for supplying electric power for electrical loads connected to a power grid; a control unit, configured for controlling the operation of the supply means in a first operating mode and in a second operating mode, wherein the second operating mode is an autonomous operating mode in which the control unit controls the energy supply device independently of external control signals; an interface, configured for receiving and for routing the external control signals to the control unit, wherein the control signals are indicative of the manner in which the supply means works in the first operating mode; and a communication monitoring unit which is coupled to the interface and the control unit and which is configured (i) to monitor whether the external control signals are received by the interface, and (ii) if, for a predetermined period of time, no external control signal or no valid external control signal was received by the interface, to transmit an operating mode control signal to the control unit which induces the control unit to operate the supply means in the second operating mode; characterized in that the energy supply device is configured, if, for a further predetermined period of time, valid external control signals are received: to receive a diagnosis start signal by means of the control unit; to transition the supply means from the first operating mode to the second operating mode; to collect diagnosis information which is indicative of operating parameter values of the energy supply device in the second operating mode; and to transmit the diagnosis information to a superordinate control device. a supply means for supplying electric power for electrical loads connected to a power grid; a control unit, configured for controlling the operation of the supply means in a first operating mode and in a second operating mode, wherein the second operating mode is an autonomous operating mode in which the control unit controls the energy supply device independently of external control signals; an interface, configured for receiving and for routing the external control signals to the control unit, wherein the control signals are indicative of the manner in which the supply means works in the first operating mode; and a communication monitoring unit which is coupled to the interface and the control unit and which is configured (i) to monitor whether the external control signals are received by the interface, and (ii) if, for a predetermined period of time, no external control signal or no valid external control signal was received by the interface, to transmit an operating mode control signal to the control unit which induces the control unit to operate the supply means in the second operating mode; (i) to monitor whether the external control signals are received by the interface, and (ii) if, for a predetermined period of time, no external control signal or no valid external control signal was received by the interface, to transmit an operating mode control signal to the control unit which induces the control unit to operate the supply means in the second operating mode; characterized in that the energy supply device is configured, if, for a further predetermined period of time, valid external control signals are received: to receive a diagnosis start signal by means of the control unit; to transition the supply means from the first operating mode to the second operating mode; to collect diagnosis information which is indicative of operating parameter values of the energy supply device in the second operating mode; and to transmit the diagnosis information to a superordinate control device. to receive a diagnosis start signal by means of the control unit; to transition the supply means from the first operating mode to the second operating mode; to collect diagnosis information which is indicative of operating parameter values of the energy supply device in the second operating mode; and to transmit the diagnosis information to a superordinate control device.