Isolator Fan Question

[RichTheRed]

This may be a stupid question, but I've always lived in older houses that never had Isolator fans. The question is, if the fan is switch to on, I assume the fan is linked to the light switch, i.e. turns on when light is turned on and turned off after the slight delay following the light being turned off.

Is my understanding of this correct. What kind of delay would you expect?
I have moved into a new house and the fan doesn't seem to be turning itself off when switching the light off.

Any guidance would be great.
Thanks

 

[Hoagy]

You're correct about the way the fan is linked to the light switch. The isolator is only for maintenance and should normally be left switched on.
The time delay is adjustable in the fan itself, how long it should be running for depends on the size of the bathroom, anything from 10 to 30 minutes would be normal.
If the fan is continuously running it's probably faulty, presumably it's still under warranty?