Hi Karl,
Yes the engineer called yesterday,very pleasant chap, ran his tests, checked the connections on and so on, box had a wobble while he was doing so, so he replaced the box.
All going well at present so hopefully problem solved.
Only time will tell.
Still think the whole process is a bit unnecessarily complex, I would much rather have just returned the box for a replacement than take half a day off work.
I trust I won't be charged for this visit?
Thanks for your help.