function of whether burner 66 is fired or not it is wrapped around shaft 74 in the direction indicated so that spring 82 places a torque on shaft 74 in the direction of opening damper 72 spring 82 is firmly anchored to the structure of water heater 60 at one end and connected to cable 76 at the other the spring and attached cable should be maintained taut with no significant play or slack preferably lubricated coaxial sheathed cables are used for this purpose mechanical spring 86 is located outside of heating chamber 64 spring 86 also has tight connection points and linkage and is firmly attached to shaft 74 of flue damper 72 after making at least one full turn in the direction indicated this places a torque on shaft 74 tending to close damper 72 in operation when burner 66 is on spring 82 is heated above the shape recovery point crystal structure transformation contracts and has increased spring force attached cable 76 has increased tension which overpowers spring 86 and causes rotation of shaft 74 to the damper open position when burner 66 goes off spring 82 relaxes and reduced tension in cable 76 allows spring 86 to overpower spring 82 quickly closing damper 72 and conserving energy the damper is closed in approximately one second thereby realizing virtually all of the efficiency gain available by closing damper 72 in the event of failure of either the flame to ignite or.