A furnace is provided with a flame rollout protection system which operates through an existing excess-air control pneumatic circuitry to shut down the furnace in the event of a flame rollout condition. A fusible tube is attached at its one end to the pneumatic system and extends into an area which will be exposed to hot gases in the event of a flame rollout condition. A melting of the tube by the hot gases causes the pressure therein to drop to ambient pressure such that of the pneumatic circuitry responsively causes the furnace to shut down. The tube is also extended to pass through an area which will be exposed to hot gases in the event of a blocked vent in the furnace, thereby causing a similar shut down of the furnace.