Just in time for Aussie Summer I have fixed the problem and now have heat in the cabin,
In Tuning for Speed by Phil Irving, he strongly recommends that everything you do is documented so you can review and compare. I should have put this in to practice!
I had done so much in trying to find the solution that over time I forgot everything I’d done.
Water pump, Control Board checked,Thermostat, Auxiliary pump, Dual Flow valve, Radiator, Top Hose - all these parts were faulty. Flushed heater core both directions. still no heat! THEN I realised that I had only flushed the return line and core but not the two inlets! With garden hose attached there was an initial hesitation before water freely flowed through both pipes. Eureka! reconnect everything… still no heat! …… A local Jag parts man asked me if I’d used a genuine Bosch valve or a Chinese copy. I couldn’t remember until I went home and looked up my paper work. Sure enough, I’d gone for a AUD$70.00 Chinese version. “Lucky” Phil the parts man said they don’t use these any more as they are very unreliable; He was talking approx. $300.00 for a Bosch. Anyway ….I made up an adaptor so I could leave the valve in place but test the flow under water pressure… again after a sluggish start I now had water through the valve…Everything reconnected AGAIN…… and I now have heat through the pipes and of course heat in the cabin… So, there was more than one problem in the cooling system / coolant flow system. I will monitor the current valve and replace with a Bosch if my problem reappears. On the air side I found a blend door actuator out of calibration and not connected. I fixed this today so looking forward to some quality time with my S. This has been a test/fix over time…All the more reason for me to have kept a note book! We live and learn.