After fussing around for fifteen minutes making phone calls back to base he says he can't fit it because the flue is too close to the boundary so he picked it all up and went on his way.
He says he cannot install it because the flue needs to be 60cm from the boundary and it's only 50cm so 4 inches too close.
The boundary is a chain link fence, there is a 50 metre garden between my place and the nearest house.

He said the only way round it is to go vertical up through the roof which would mean extra unspecified cost.