A system and method are disclosed for high temperature protection of combustor and other components by controlling the temperature of combustion chamber gases in a fuel cell system tail gas burner using a nozzle or plurality of nozzles to inject water or water vapor upstream, downstream or directly into the combustion chamber. A variable speed pump, actuated valve or other flow metering device regulates the supply of water or water vapor to the nozzles. For the case of water vapor, an evaporator is required between the pump and nozzles. Flow regulation is effected by a control algorithm that reacts to combustor temperature, changes in the power production of the fuel cell system and/or other related system parameters.