The outflow of coolers or water transport plates of a fuel cell stack (15) is fed to the inlet of a gas/liquid separator (12), the liquid output of which is connected through a primary pump (11a) to a liquid accumulator (21). A secondary pump (44) connected to the liquid output (20) of the liquid accumulator is fed to the principal inlet (31) of an eductor (32), the secondary inlet being connected to the gas output of the gas/liquid separator. The outlet (37) of the eductor is fed through a conduit (38) to a point below liquid level in the liquid accumulator. Thus, failure of the secondary pump (44) will not cause cavitation of the primary pump (11a) through the eductor so that coolant will continue to flow through the fuel cell stack. A demineralizer (26) is fed through a pressure reducing orifice (25) from the outlet of the secondary pump.