Apparatus for the thermal utilization of a primary fluid, said apparatus comprising: a) a heat exchanger device with an inlet line, through which primary fluid is able to be conducted to a heat exchanger unit by means of which the temperature of a secondary fluid is controllable by the primary fluid, and having an outlet line, through which primary fluid flows out after flowing through the heat exchanger unit; b) a flow line, through which primary fluid is able to be conducted past the heat exchanger device in terms of flow such that said primary fluid does not pass to the heat exchanger device; c) a control and regulating device (58, 72), by means of which the particular amount of the primary fluid that passes to the heat exchanger unit and into the flow line is able to be set; d) a safety device, by means of which the flow of primary fluid to the heat exchanger unit can be interrupted, wherein e) the safety device comprises a first valve unit arranged in the inlet line of the heat exchanger device, the inlet line being selectively closable or openable by means of said first valve unit and operating means being required for the operation of said first valve unit; f) the first valve unit is set up such that, if the operating means are absent, it takes up its closed position; g) the safety device also comprises a safety system (58, 62), by way of which the operating means for the first valve unit are able to be disabled; h) moreover, a second valve unit is arranged in the outlet line of the heat exchanger device, characterized in that, i) for the operation of the second valve unit, operating means are required and the second valve unit is set up such that, if the operating means are absent, it takes up its closed position; j) the control and regulating device (58, 72) comprises a fan, the operating output of which is settable. a) a heat exchanger device with an inlet line, through which primary fluid is able to be conducted to a heat exchanger unit by means of which the temperature of a secondary fluid is controllable by the primary fluid, and having an outlet line, through which primary fluid flows out after flowing through the heat exchanger unit; b) a flow line, through which primary fluid is able to be conducted past the heat exchanger device in terms of flow such that said primary fluid does not pass to the heat exchanger device; c) a control and regulating device (58, 72), by means of which the particular amount of the primary fluid that passes to the heat exchanger unit and into the flow line is able to be set; d) a safety device, by means of which the flow of primary fluid to the heat exchanger unit can be interrupted, e) the safety device comprises a first valve unit arranged in the inlet line of the heat exchanger device, the inlet line being selectively closable or openable by means of said first valve unit and operating means being required for the operation of said first valve unit; f) the first valve unit is set up such that, if the operating means are absent, it takes up its closed position; g) the safety device also comprises a safety system (58, 62), by way of which the operating means for the first valve unit are able to be disabled; h) moreover, a second valve unit is arranged in the outlet line of the heat exchanger device, i) for the operation of the second valve unit, operating means are required and the second valve unit is set up such that, if the operating means are absent, it takes up its closed position; j) the control and regulating device (58, 72) comprises a fan, the operating output of which is settable.