Fingers crossed but both now repaired and on their way home
Both receivers problem was with firmware. Yamaha technicians just reinstalled and both seem to be working.
Yes, yes best to update via Ethernet cable or usb BUT and it's a really big BUT!
Both receivers automatically updated by wifi when setting up again after moving house. No option to skip, no yes, no, remind later. Both just updated when setting up.
Technician isn't impressed because they can't see how to turn off auto update.
Bottom line. If there's problem updating by wifi it shouldn't be automatic or even an option.
Good news. No service fee just shipping
Thanks for all input, suggestions. Greatly appreciated