I said aw god, if that's a k series it sounds cooked, possibly headgasket... I go to have a look and you would NEVER guess what it was!!
Coolant cap was sat on the battery!!!!
I have never known luck like this,, in short I filled with coolant and squeezed hell out of the pipes for ages, heaters on and hot for over an hour I repeated the process. All pipes heating up except 1 of the matrix pipes, took it for a run with a heavy foot and all of a sudden heaters... Been fine since!!!
1 lucky girl and 1 lucky K series



