How do you fix a second floor bathroom leak coming from the bathtub water valve when turned on when water is dripping through the fan vent to the bathroom below creating a wet spot on the floor?

Fixing a leak You should first check fan vent outlet on roof - should have a flapper of some kind that may be stuck open or have a hole in it. If it only leaks when it is raining that is first clue. One other possibility is the vent pipe is running through cold attic causing condensation - you can wrap vent pipe with insulation to solve that one . Shorten distance of fan vent, too much condensation to evaporate before running back to fan.

More input from FAQ Farmers:

• It isn't possible to fix a leak unless you know where the leak is coming from. It could be from the bath, basin, radiator, toilet. We need more information.

Fix the bathtub water valve first, since you know it is broken. If you have a plumber do this, he may be able to diagnose what is happening with the fan. Recently, we found that the condensation pipe was plugged, and we got a leak--the water always finds a path.