Well final update from me, as finally as of this evening all is sorted. Not without some final dramas though.
After Vaillant agreed on a suitable repair I managed to get an electrician out on Monday to reroute and extend the cable to correct place and sort out the hole that had been drilled.
Vaillant then came back out today to reconnect the boiler, only to find that the guy who ID’d it in the first place had also **** one of the pipes trying to cap it off. Long story short I then had to get another local company to come and sort that out, only for them to then find the electrician hadn’t quite wired it up correctly which they did resolve.
In total it’s taken best part of 2 weeks to resolve but at least it hasn’t cost us too much in the end. Thanks everyone for the advice.