Had the call. He explained how to access the service menu, which allows a Factory initialise. Ran it, and no luck (note though this takes a lot longer than the Power and - button reset, so may help with other issues)
He said if it doesn't work will need the main board replaced. So calling back now.
To access the service menu, press the following buttons in order, quite quickly:
Then SVC appears on the front panel, after a while for me, again just the background graphic, but pressing Display shows a blue service menu with options there.