good fans, but not optimal wind protection flaps

Hello There,
I have the fan for 5 years with no problems in use.
However, I have found that the valves designed to prevent air into the room from flowing back (cold) does not close, reliable. For the flaps are too light and the angle at which they are built, too steep. I've checked several times with a flashlight when fan off, because I had the impression that cold air enters the room. Time the flaps were closed, sometimes one or both flaps were open. I have now complained each flap with a small weight, so that they close better and the fans it can still impress easily when it starts. An electric shutter would be better, but that there is not the model piano unfortunately.