Re: bathroom fan ?
Re: the damper that MLB mentioned, I've seen it get stuck on more than one occasion. Basically, the water vapor, paper & skin dust, and probably who-knows-what-else is sucked up by the fan. Some of that ick sticks to the internal parts of the fan, including the damper. Eventually enough builds up so that at some point when you turn off the fan, the damper closes and never opens up again.
Remove the grille, unplug the fan unit and remove the fan assembly from the housing. You should then be able to access the damper which you can then get unstuck.
While you're at it, give all the parts a good cleaning. You may be able to disassemble the motor, clean the shaft and bearings, reassemble and lubricate with light machine oil (such as 3-in-1).
Just do it. It's not that hard, and it needs to be cleaned anyway.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.