Follow the instructions in this article to set up the Sub:

https://support.sonos.com/en-us/article/set-up-your-sonos-sub

Ofcourse I have been following all instructions, the arc and era’s are working but the sub can not be connected. I have been reading the community reports and many people seem to have the same problem. It’s very frustrating 

Try unplugging the Arc and Sub from power for a couple of minutes and reboot your router and phone. Also be sure WiFi is enabled on all speakers in the Sonos app.

I have done this including  resets at least 20 times…. Chatted with the sonos “ help” service, spoke with an ignorant sonos helpdesk lady….. it’s  not the product but the wifi answers etc.

all other equipment including my central heating are running on the same system without any problem… except the sub

Have you tried temporarily wiring the Sub directly to the router with an ethernet cable before you start the setup process?

I did…. And then the whole system is down….

1. Is the Arc wired to the network? If not then don’t wire the Sub. Doing so will cause issues.
2. Are the Era100s connected as surround speakers? Do they work okay?

What error messages are you getting? What happens when you try to bond the Sub to the Arc? 

Dear Ratty

no the arc is not connected via an ethernet cable but works well on the wifi as welk as the era’s as surround speakers…. All is visible via the sonos app……except the sub…

btw … thks for your attempts to help….

What messages do you see in the app? The Sub should work, unless of course it’s faulty.

Factory reset the Sub, then see if you can add it successfully.

No error messages, when it is connected i get the message that it is installed but if it is not visible it should be un and replugged ….and then the whole circus starts again 

Restart your network. Router first, then everything else.

The dealer rep will come again ( for the 3 rd time ) tomorrow… the sonos help desk only works from monday to Friday during office hours…..

and the sonos rep seems to be on holiday….

what kind of a company is this?

Have you got the Era 100’s set up as surrounds, or as a second room?

If you go to Settings (the gear wheel at bottom right of the screen in the app), then System, you should see your room listed. It should say something like Lounge (or whatever room name you’ve used) and then (LS+RS+Sub)   If it doesn’t say that, what does it say?

Are you sure you added the Sub to existing system rather than new system?

Same room arc ls and rs are there but sub not connected, can not find the sub is the message 

In that case it’s quite likely not setup on your system. Have you factory reset the Sub and got it to show a flashing green status LED as mentioned in this support link?…

https://support.sonos.com/en-us/article/reset-your-sonos-product

If so, with its LED still flashing green, first fully close/re-open the mobile Sonos controller App and then goto ‘Settings/System/Add Product’ - and follow the instructions to get the Sub setup and added to the Arc Room and then see if it works whilst playing any music/sonos radio station etc.