Fuel cell system and method for operating a fuel cell system

The system has at least one fuel cell and a heater downstream of the fuel cell(s) that receives the outlet flows from the fuel cell and contains an evaporator in the flow path of an output medium for providing an operating medium for the fuel cell. There is an arrangement for regulating the temperature of the vapor of a first medium evaporated in the evaporator or the temperature of a heat carrier medium of the evaporator to a defined temperature. The system has at least one fuel cell (2) with an anode chamber and a cathode chamber, a first medium feed line (13) to the anode chamber, a first outlet line (3) from the anode chamber, a second medium feed line (14) to the cathode chamber, a second outlet line (4) from the cathode chamber and a heater (5) downstream of the fuel cell(s) that receives the outlet flows. The heater contains an evaporator in the flow path of an output medium for providing an operating medium for the fuel cell. There is an arrangement for regulating the temperature of the vapor of the first medium (7) evaporated in the evaporator or for regulating the temperature of a heat carrier medium (8) of the evaporator to a predetermined temperature. Independent claims are also included for the following: a method of operating a fuel cell system.