wiring a bathrom fan

so I have a Manrose extractor fan and I’m trying to replace an old fan which is running through and isolation switch and controlled by the main pull bathroom light switch, I had it setup properly before somehow but the timer function was not working, I’ve been trying and trying and with the...

Any ideas/help. We are renovating the bathroom where all wiring is in the loft and over boarded so cannot get at. The lighting circuit is wired via a junction box somewhere under the floor. So only exposed wire is the live/neutral for the pull switch and at the other end, live/neutral of the...