I think I have sorted my indicator light problem.
Rebooted the main box in the lounge a couple of times but indicator light still went off completely. However on the last reboot I got an onscreen warning of poor ethernet connection. We live in a bungalow and the Hub3 is in one of the bedrooms. The V6 boxes are in the lounge and another bedroom. The main TV box in the lounge is/was connected to the hub via a VM supplied Netgear Powerline adaptor. I double checked all the cables and had 3 good lights on both plug in adapters.
I disconnected the ethernet cable from the main box, went into diagnostics settings and reset the box to the WiFi signal and the indicator light fault has cleared.
It would appear that the wifi connection is better than the powerline ethernet one.