Abstract: A fuel-fired water heater has a combustion chamber disposed above a wall ucture forming a flow path for combustion air being drawn into the combustion chamber during firing of the fuel burner portion of the water heater. A combustion air shutoff system is incorporated in the water heater and functions to sense an undesirably high firing temperature in the combustion chamber and responsively shut off essentially all further air flow to the combustion chamber and thereby terminate combustion therein. In various disclosed embodiments thereof, the combustion air shutoff system includes a damper member movable between an open position in which its permits air flow through the combustion air flow path, and a closed position which it blocks essentially all further air flow through the combustion air flow path. The damper is releasably held in its open position by a eutectic metal fusible link member positioned exteriorly adjacent an exterior wall of the combustion chamber.