I noticed some dirty water that had dripped down my tiling and into the bath from my extractor fan. Then I noticed that the exterior wall, directly under the extractor fan vent was quite wet and spreading downwards and outwards. The vent is a louvre type with no external cover. I did wonder whether it was driving rain that had caused this but the fan is not in an exposed position and this has never happened before in 5 years. Any advice gratefully received. Thank you.