Got a bathroom fan thats been there since the house was built (only 7
years ago). Its got a pull string switch as you go into the bathroom
and the fan is on the opposite outside wall.

Been working fine until one day when I turned it on it tripped the
circuit breaker. My circuit breaker is in the garage and has got a
main switch as well as switches for upstairs/downstairs lights,
upstairs/downstairs sockets etc - it tripped the upstairs lights one.

Tried again - tripped again.

So far, I've :-

1. Replaced the pull switch - still the same.
2. Replaced the entire extractor fan unit with a new one - still the
same.

I'm afraid thats the limit of my electrical knowledge now. Anyone got
any ideas ?