the invention relates to a cooling system for a fuel cell , comprising a main heat - transfer - fluid circuit including a circulation pump and a heat exchanger with the exterior , which feed an upstream pipe supplying the fluid to the cells of the fuel cell , said fluid leaving the cells via a downstream pipe in order to return to the main pump . the invention is characterized in that the main circuit comprises a three - port controlled valve on each upstream and downstream pipe , the third available port of the upstream pipe being connected to the inlet of the pump and the third available port of the downstream pipe being connected to the outlet of the pump in order to establish a secondary fluid circuit .