So the latest post pulled me back to this thread and I realise that I didn't close this out wrt what happened when I swapped the unit back in, all be it with a new power supply.

In a nutshell, everything was fine with the unit. It booted up, connected, yadda yadda, all without issue. To be clear, no firmware fun was required. The unit was OK, the power supply had failed.

So if you have a 2710 and all lights start flashing (not just the top two) and, if you listen carefully, you here a relay cycling (clicking), suspect the power supply.

HTH someone.

Fat Freddie's Cat

So can I say a huge thank you to Jedi, Fat Freddie's Cat and all who've contributed to this thread.

A year later I powered down my 2820Vn whilst I re-routed a telephone cable under the floor. On power up all lights flashing, bar dsl. Various power cycles resulted in lights pulsing and clicking sounds. Looked like the router had bricked itself. arhhhhhhh £200 pound out of warranty plastic brick.

I spent several days trying to figure out what had happened. Read lots of posts about factory reset - reloading firmware. Tried and tried everything but could not get the router in TFTP mode. I was about to purchase a new 'cheaper' router; but pulled back. Then the next day I found this thread, I took my router down to a local electrical shop and found a PSU unit; in store tried it... and WOW it booted;

You've helped me where DrayTek support were unable to .....

Thank you ... thank you ... thank you... this should be on a FAQ.

Just amazing.... thank you.