Fuel cell system

A fuel cell system comprising:

• a plurality of fuel cell units;
• a cooler;
• and
• a controller,
• wherein
• each of the plurality of the fuel cell units comprises:
• a fuel cell stack;
• a supply passage for supplying refrigerant from the cooler to the fuel cell stack;
• a return passage for returning the refrigerant which passed through the fuel cell stack to the cooler;
• a circulating passage connected to the supply passage and the return passage, the circulating passage being for returning the refrigerant in the return passage to the supply passage;
• a switch valve configured to set a destination of the refrigerant flowing in the return passage to one of the cooler and the circulating passage;
• a first temperature sensor configured to measure a temperature of the refrigerant in the supply passage at a position upstream of a merging point of the supply passage and the circulating passage;
• a second temperature sensor configured to measure a temperature of the refrigerant in the supply passage at a position downstream of the merging point;
• and
• a third temperature sensor configured to measure a temperature of the refrigerant in the return passage, and
• when measured values of the first temperature sensors of the plurality of the fuel cell units do not match, the controller is configured to provide notification about malfunction of the first temperature sensor of at least one of the plurality of fuel cell units.