Out of luck ... looks as though there is no config data there. I probably cleared it all before moving to PPPoE.

It should work very easily .... have you thought about resetting to factory and start again?

In reply to a post by Pheasant:

I’d just completely uninstall all that third party firewall junk. It’s honestly more trouble that it’s worth. The built in gear is all you need.

Seconded. Major corporates have all done the same.

In reply to a post by pet_griffin:

Hi tdw42 . yes, the USG will make a PPPoE connection and has an IP address and DNS servers set by the WAN but that's as far as it goes. Just wondering now if this is an issue with AVG firewall - that was stopping me from seeing the UI network until I set the network to be "trusted". Let me try that over the Xmas hols ...

Given the USG is connecting, gets a WAN IP address and sets DNS correctly it points to one of two possible issues;

1. Firewall / routing on the USG - or the lack thereof - as the clients can’t ‘get out’ to internet from behind the USG - but given that other folks here are saying the default USG setup just works, out of the box, them default firewall and NAT setup should be good to go. Which then strongly points to…

2. A client device issue (noting your previous issues with AVG)

Now if you have another (hopefully dissimilar type/operating platform) client device you can check connectivity with the USG in place - like perhaps a tablet or phone or at a pinch boot that windows box with an Ubuntu stick - then this will prove or disprove both (1) and (2) above.

So, some progress.. I turned off the AVG Firewall on the laptop running the UniFi controller and was able to make a PPPoE connection via the ECI modem - hurrah! I then disconnected the PPPoE connection, plugged in the (adopted) USG and was astonished to find I still had internet connectivity. Unfortunately things then went downhill. For some reason the UniFi controller won't run on my Windows 7 PC - a DOS window pops up, flashes an error message and then disappears before I can read it but I think it is Java-related. I connected the Unifipi controller to the network but this would not accept my Unifi credentials. I also reset the gateway IP address on the USG to 192.168.0.1 to match the gateway on the old network but then lost the internet connection. I tried running the controller on my Win 10 desktop so that I could then connect it to the new network but that messed up the network card settings and the only cure was to update the card driver. I am currently uninstalling the AVG stuff from the laptop and will then start again once I find out why the Unifi controller won't run

That’s positive progress despite the setbacks.

I think your problems really now centre on having a stable UI controller on the network. To that end…

On the Win 7 box, you might want check and ensure your running the latest Java 8 update and any other possible updates (given Win7 is now out of support by MS) possibly the reason why you are getting runtime errors with the UI controller software.

The UnifiPi controller needs to be fully patched and updated too. You may need to logon using any local credentials you used in the setup before synchronising the logon with the UI cloud credentials. You might have a sort of circular problem with this until you sort out your internet access via the USG.

Remember when swapping controllers about, you need to correctly migrate your settings from one controller to the other - to preserve all your settings and keep everything nicely in sync otherwise you are circling around on yourself. See this vid on YT as this chap migrates his setup between controllers.

Personally for this job I like the small plug and play UI ‘appliance’ like the original UniFi Cloud Key, still available for under £80 or the later Cloud Key Gen2+. You just plug them in and they work.

In reply to a post by Pheasant:

On the Win 7 box, you might want check and ensure your running the latest Java 8 update and any other possible updates (given Win7 is now out of support by MS) possibly the reason why you are getting runtime errors with the UI controller software.

The controller doesn't care about the underlying OS, the Windows version can get confused if both the 32 and 64 bit versions of Java are installed.

... the original UniFi Cloud Key, still available for under £80 or the later Cloud Key Gen2+. You just plug them in and they work.

Whilst the original Cloud Key is still available the OS is woefully out of date, Debian Jessie which went EOL at the end of Jun 2020, so no patches for any SSH, SSL, DNS, nginx (for the CK web UI) or other non-controller components. Ubiquiti have a track record of not bothering to patch/update old libraries in applications either, even when not directly exploitable these can provide a stepping stone in a chain of vulnerabilities.

OK, I think we're there .... I have my new UniFi network connected via a USG attached to an old ECI modem. in case anyone else has the same issues this is what I did.
1. Uninstall third party firewall software on laptop where UI controller will be running.
2. Connect to laptop to internet. I did this via PPPoE to try to minimise subsequent IP addressing issues and conflicts between the old and new networks
3. Create Ubiquiti user account
4. Upgrade Java to latest version. I am running Win 7 Pro so upgraded to the latest 64 bit version
5. Download and install latest version of UniFi controller (as administrator)
6. Create a new Unifi network configuration.
7. Disconnect from PPPoE. Connect the modem WAN cable to the USG WAN input and the laptop (with controller still running) to the new network.
8. Hopefully, the new network devices will now all show up and be ready for adoption
9. Adopt the network devices, upgrade firmware where appropriate and enjoy! Machines running a 3rd party firewall might need to be adjusted (eg "trust" the current network) to allow WWW access

I'm sure that there are improvements that could be made but this worked for me. Still a little nervous about the controller so have ordered a CloudKey Gen2+. Just wanted to say a massive "thank you" to everyone who contributed to this topic, especially @Pheasant. HNY all!!

Good stuff. Glad it’s working for you. 👍