Just to add, filled up again this morning, another Brim, and all is good, sweet, LPG kicks in as it should now, even on a luke warm engine thats been stood for a while. will still be doing some planned flushing as still a lot of crap floating around plus I need to get some proper coolant in there. Haven't ruled out the re plumbing, but just too cold at the moment, may be another final reverse flush of the Matrix and Vap and we'll see.
So, end of the day a relatively cheap fix, some Soda Crystals and Dish Washer Tabs
so the moral of the story, if there is one, is keep the coolant clean and up to date, especially if your not using LPG on a regular basis.
I cant help wondering what a LPG specialist would have done or charged for a fix, if any, anyway well pleased so far, and enjoying really cheap motoring, a be it a 6'2' driving around in a 1.2 Noddy Van.
Thanks all for your input and help.