This part saved me hundreds of dollars. Problems began with maintaining the temperature in different zones. The service engineer suggested adding a door between the upper and lower floors. (At least 10 years without previous releases). I fixed the problem myself and found that the motor turning the flap to the open position was not working. No channel swaps, no new damper and no big bills. Just a small motor with a set screw saved me hundreds. Works like a charm and very easy to fix