Can't connect. Getting PADO errors, PlusNet say no fault found...

[#1]

Last Sunday (Feb 1st 2015) evening I couldn't establish my FTTC connection to PlusNet. It's worked perfectly since installation, and was fine on the previous Friday when I was working from home all day.
The syslogs on my TP-Link Archer C8 router show the error as a "Timeout waiting for PADO packets" when trying to establish the PPPoE connection. Nothing changed at my end between Friday and Sunday. I've tried 3 different cables between the router and the Openreach (ECI) modem, and also a different router (Billion 7800N) that I used previously.
I've also tried various resets of modem and router including leaving the router turned off for a period (> 1 hour), in case it's a lockout due to excessive retries.
PlusNet reported NFF, but that would just mean the modem was connected and the line was OK, not that the PPPoE session could be established.
Any ideas? Is it likely to be a faulty modem? Or a fault at the exchange? Any further tests I could run?
Many thanks,
Antony.

[#2]

Can you try reconnecting now for me?

[#3]

Hi Chris,
Sorry I'm at work at the moment. I'll try when I get home this evening. Thanks for the text message!
Can you give me a hint what you've changed?
Many thanks,
Antony.

[#4]

It's something I'd have expected the faults team to pick up on. Basically from our side we could see an ongoing connection, which doesn't fit with your comments of testing different routers etc. So I've ended that session on the BTWholesale side, which should now allow your router to connect back up.

[#5]

OK, that's odd. I don't normally leave my router turned on when I'm not using it (it was turned off when I left the house this morning). I do leave the Openreach modem turned on 24x7.
Shouldn't BT's equipment drop the session automatically? Is this likely to be a one-off? Or is there something I can do to fix this if it happens again? Would it be better to leave the router on and connected 24x7?
Thanks again for your support,
Antony.

[#6]

It's rare that this happens, and as far as I'm aware there's nothing specific you can do from your side to stop it happening unfortunately.