Oh how embarrassing. .... it was my own fault... on my 4.2 tdi I coded in Auxiliary heating because even without the burner, the 4.2tdi has electric heating in the vents because of length of time it takes to heat up the iron lump. The S8 does not have the electronic elements like the tdi. So when I coded it in, it shut off the valves for the coolant to flow to the cabin. So I've coded it out and all is good now
700+ ponies under the bonnet and no heating, what a disaster....