Extractor fan shutters sticking

[stuart noble]

Anyone had this problem? It's a 4" bathroom fan and the external grille has

3 flimsy plastic shutters which keep fouling each other so that they stick open. Can you buy separate external grilles? As the wall in question faces due north I'd like to install something that is genuinely draughtproof when the fan isn't switched on. Any thoughts appreciated.

[Dave Stanton]

Ours does this when the wind blows from certain directions, thought a bot fitting some type of spring to it.

Dave

[Set Square]

In an earlier contribution to this discussion, stuart noble

[stuart noble]