Fuel cells are very well suited for the cogeneration of power and heat. An adaptation of the fuel cell power to the thermal requirement of the live load results in faulty adaptations and efficiency losses if the thermal requirement fluctuates significantly.The invention aims to achieve a continuous and lossless adaptation of the thermal production of the fuel cell to the current thermal requirement.The invention utilizes the fact that fuel cells are continuously adjustable over a broad load range. The invention proposes a continuous control of the current based on the supply or return temperature of the thermal circuit. According to the invention, a control method is used that has a quasi-continuous characteristic, particularly a control according to a PID-algorithm with additional limitation of the current as a control variable with respect to the minimum and the maximum value and of the amount of the time rate of change of the current. Such a control allows the fastest possible adaptation of the cell power to the respective thermal requirement.