RubberBiker wrote:
My Rayburn installer cautioned me about insulation in close contact
with the back - reckons it can get significantly hot at times.

I've had mine stood out well from the wall, so that there is a
substantial bit of studwork faced with cement board and the kingspan
some distance back.

If I didn't have the space to do this, I'd probably use rockwool
rather than kingspan.

Actually a couple of layers of Masterboard are probably better than nothing.