Chris Green wrote
| Owain wrote:
| The air that the fan extracts from the bathroom has to be replaced
| from somewhere. Possibly it is being replaced, not by air from your
| own hall, but by air being sucked from an adjacent flat. I'd have a
| look at the boxing-in of pipes esp the soil stack and underneath the
| bath panel.
| Exactly what I've just said (differently)! :-)

A combination of great minds and off-line newsreaders.

Owain