I think I have realised what has happened. I need to trace back the wiring to confirm this, and it is something which long term needs sorting properly. There was a 6mm cable feeding an immersion heater in the bathroom. When the contractors fitted the central heating system they said they would need to come back to remove the old circuit, they never did the circuit was live for many years.
When my mate fitted a new bathroom 10 years ago I discovered the cable was live and just sat there behind the bath!!!! My mate then suggested wiring an extractor fan into it, so we did and replaced the 13amp fuse with a 3 amp one.
Around 5 years ago my dad was doing some drilling and then the DNO fuse blew, we had to get them out to replace it, we never bothered getting the cable fixed and just removed the fuse in the CU as a tempory measure with a note on the CU saying the cable is damaged (and where).
As there is no FCU's apart from the old for old immersion heater in the bathroom I wonder if the circuit in the bathroom is taken from this old cable and hence no longer works?
I will try and trace the wiring to see where it goes, I suspect if that flex was powered from the ring main there really ought to be a FCU for it as it won't be protected otherwise, 1.5mm flex protected by a 32amp fuse is not good
There is a FCU next to the boiler, but as far as I am aware that is simply for the timer and boiller circuit.
I realise he damaged circuit needs disconnecting from the CU, but a PIR will be required first as I am sure there are more important issues such as poor earth bonding etc.
The now dead extractor fan in the bathroom is probably completely none compliant too, no RCD, probably not in a safe zone etc and probably was never compliant (it was at least done a long before the part p regs changed) but I now have doubts it ever even complied with the 16th edition. I am a lot wiser now though, and realise joiners (my mate) should not touch electrics.
