Thanks guys, sorry for the delay in responding but for some reason CF were not sending me the usual email
notifications that I had other replies.
This is 'all' very helpful.
If the 'header tank' that came with the Luxford is meant to operate with as little air as possible, therefore filled up, then I was meant to add the extra tank as others recommended.
But am I right in my logic that I should have just purchased a heat exchanger
without the header tank and then fed that from the original volvo
This seems to be working now. I'll go for and extended sail over the weekend and really test it out over some hours, but I'm pretty sure this has fixed the problem. But I'm still ignorant of why the heat exchanger
has it's own header tank if I then have to add this second 'overflow' or 'expansion' tank.