At long last I got the fan (timer/humidity) running. From previous post re electrics I got an electrician in who found the problem was where they had taken the permanent feed from thats what threw me.
Anyhow assuming the fan is not faulty and the elec wired properly it doesnt turn off with the hum/timer was running for 40 minutes even after I adjusted the timings.
I did try reversing the permanent live and switch live but that just makes it operate on/off with the light switch. The shower room wasnt used for over 24 hours so assuming it was not too humid.
Any other ideas to try.