Hi michael, if your powertouch fitter just left the isolator switch under a bedbox phone up powertouch and complain, (he's just been a lazy sod) ask for a different fitter to come out and fit the switch where it is supposed to go, which is in the battery box, below the 240v input socket.
The reason it is put there is so that u can leave your door open to get to the switch quickly if things go wrong.
It has been known on all of the makes for a relay to stick/freeze and u cant stop the van running away, if u cant switch it off.
You would have to jump in front of it to pull on the handbrake and then disengage the rollers from the wheels, then remove a battery connection.
U still will have to on a carver mind as they dont supply an isolator switch.
Also some times they need a reset which they can do automatically, if u remove them from the mains for a couple of mins.
I worked for powertouch as an area fitter for a couple of yrs so i do know.