Try resetting the Sub. Then go into the Arcs settings and select Connect Sub. It should pair the Sub with the Arc. 

Hi Pools 3015.

Thanks for your help... I've done that numerous numerous times... I've removed/added/reset both arc and sub. Connected to same WiFi. Uninstalled and reinstalled sonos app... 

The Sub shouldn’t be connected to your WiFi, it should be bonded to the Arc. When you ‘bond’ a Sonos sub, it is, at that point, connected via a hidden 5Ghz channel to the Sonos device it is ‘bonded’ to. It does receive a proxied IP address from the router through the Arc, though. 

How is your Arc connected to your WiFi? Is it via a 2.4 GHz signal, or a 5Ghz signal? Have you tried, at least temporarily, connecting your Arc to your router with an Ethernet cable?

Please don’t do ant further resets, you’re just erasing any data that Sonos might be able to use to help you.

Hey Bruce. Great advice. 

I had a feeling that the sub needed to use the Arcs "network".

I have plugged in an Ethernet cable to the arc. From my internet settings app, I can see the sub is now connected to Ethernet rather then WiFi 2.4ghz. 

Although the sub is still not working. Arc has the "enabled WiFi" selected. 

How do I "bond" the sub to the arc. I believe by "adding sub" would automatically connect the 2 devices? 

Make sure (and it may be harder to do, I’m not sure the state of your Sub) that the Sub’s WiFi is turned on too, since both sides need to connect. But I suspect it is on, but worth double checking. 

I’ve not done this process in the new app, but I think that you need to go in to the controller, select the gear icon at the top right, then select the room name of your Arc. For me, it happens to be Living Room TV.  Then select ‘add a Sub’.  It should, after that process, show the Sub in the ‘Product’ list, showing up as the two products in that room. 

You then need to be certain that your TV is sending a Dolby Digital (at least) signal to make the Sub work. Older shows (like M*A*S*H, or many talking head programs, for instance) are not recorded in a high enough format to send any data to your Sub, so do your testing with a newer action movie. 

However, if this doesn’t work for you, I’d call Sonos Support directly to discuss it.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Thx Bruce I will try the Dolby setting within the tv. Much appreciated.