Hi Shingi
Thanks for getting back, in the interim I have had a very competent electrician investigate, he has gone through system from top to bottom and all seems to be working fine, there is definitely a sequence required to operate these things, so many buttons etc.
The most significant problems, and 3 other experts who looked at vehicle and all said same, were the bolier, water pump and the inverter under O/S seat (mine is left hand drive), all transpired to be find, but I learned that the switch on the inverter should be turned off when not in use or when driving and should be turned on when plugged in on a site.
All is now ok, perhaps until the next time, it is such a relief as those 3 so called experts told me I needed to replace those 3 main components and was prob looking at atleast £1500.
Some people eh, just want to take your trousers down or perhaps they were simply incompetent, anyway all "seems" to be good at moment, did use van last weekend for two nights in Bakewell as a test run, all good.
Thanks again