a fuel processor system capable of circulating fuel processor system gases , such as reformate , anode exhaust , and / or combustor exhaust , through the fuel processor to provide a number of distinct advantages . the fuel processor system having a plurality of fuel cells discharging an h 2 - containing anode effluent and an o 2 - containing cathode effluent . a fuel processor is also provided for converting a hydrogen - containing fuel to h 2 - containing reformate for fueling the plurality of fuel cells . a catalytic combustor is positioned in series downstream from the plurality of fuel cells and a vaporizer reactor is coupled to the catalytic combustor . a bypass passage is finally provided that interconnects an outlet of at least one of the group consisting of the fuel processor , the plurality of fuel cells , the catalytic combustor , and the vaporizer reactor to the inlet of the fuel processor . the bypass passage is operable to circulate a fuel processor system gas to the inlet of the fuel processor .