You have to add the Ones to WiFi first. Then you can add them to the surround system.
open app
- Add arc. This worked.
- Plug in two One’s and put them in reset mode (green slow flash)
- In app go to settings > room > add surround > add surround (from popup) = instant “no devices found”
The step 3 above is incorrect here - you first need to add the products to the system (Settings/Add Speaker or Component) and then go onto add the two setup speakers as surrounds to the Arc.
Trouble is that when I tried that the app created another room. So I had two living rooms. But the speakers (arc > surrounds) are not connected.
I ended up with three rooms. One with the arc, one with the surrounds and one with the sub.
you should be able to move the speakers to the same room but there is no option for that.
honestly. This is crap. 
It’s too late now, but the easy way to changing WiFi is to temporarily reuse the old SSID and password, there was no need to Factory Reset. Now you must add the units to the system individually, don’t try to build a “Room”. Once all the units have been added to the system, then you can add surrounds and SUB to the soundbar. Now the surrounds and SUB are part of the surround Room.
Trouble is that when I tried that the app created another room. So I had two living rooms. But the speakers (arc > surrounds) are not connected.
I ended up with three rooms. One with the arc, one with the surrounds and one with the sub.
you should be able to move the speakers to the same room but there is no option for that.
honestly. This is crap.
It’s not crap, it’s just the way you’re presently thinking about things.
You can call the device names anything you want. So as an example, the Sonos Arc can be called ’Dining Room’, just as an example….
- The Sonos Sub can be named ..er… ‘Sub’ - it is by default anyway.
- Left Surround, let’s name that… ‘Dining Room-LS’
- Right Surround, let’s name that… ‘Dining Room-RS’
… or whatever names that suit your own preference.
When you then ‘bond’ them into one Home Theatre setup, it will all join together and will be called ‘Dining Room’ … you can even go onto rename that too, if you want.
In the system settings the bonded Home Theatre will show itself as one room - see attached screenshot.
@lukewest
Maybe this link will help you too… (this step is needed after you have added all the speakers to the Sonos system and have given them their names) …. It explains how to ‘bond’ them together via the Arc room settings:
https://support.sonos.com/en-us/article/add-surround-speakers-to-a-sonos-home-theater
It’s an almost identical process for the adding the Sub to the Arc HT too.
@Ken_Griffiths Thanks for help :-)
I’ll follow the guide that you have given me the link to.
I had to add product which put it in a new room, then I added the product to the existing system and all was good.
Many Thanks @Ken_Griffiths
