Dim lighting and fan

Fitted new halogen lights in bathroom using low voltage and dimmable transformer, the problem is now that fan timer cut off is not working when the lights have been turned off. Help!!!!

have u wired the switched live and perm live the wrong way?

You can't put fans on dimmers - you'll need to add a separate switch for the fan, you can no longer have it controlled by the lights....

John,
Mount a 240V PIR over the bathroom door so it detects anyone walking in. Set the timer on the PIR and turn the daylight sensor off. Fit a fan without a timer and use the PIR to control it.
If the fan is in the zones above or next to the bath or shower it must be a 12 volt SELV fan with a transformer.
iv'e done this in my downstairs toilet and it works a treat.

You must also have a fan isolator or an isolator to isolate the entire bathroom lighting and fan. I use a 20A DP water heater switch mounted above the door outside the bathroom.

What if he doesn't want the fan to come on just because there's someone in the room?

I've got my fan triggered by the shower, because that's when it's needed, but it's not a solution that the average person would implement. I've never been convinced by PIRs, or light-switch control, as the fan will come on unnecessarily so many times. Waste of electricity and waste of fan life.

Humidistat or just a switch for the fan and remembering to turn it on and off is the way to go...

PS - still a bit old to be replying to, Bob...