How do you have your system configured - as home theatre with sub and Ones bonded to the playbar? Which Playbar - Beam, Ray, Arc? 
What is showing in the “room” or rooms containing the speakers (look in Settings/System and tell us what it says under Products). Can you screenshot that page and include it in your reply. 
Is wifi disabled on your play bar?

I have a playbar optically connected to the tv/sky with the sub and two Ones wirelessly. It was fitted professionally and all used to work normally until recently.  All component software is up to date. All showing as linked   Just no sound at all from the sub   Thanks 

Moderator edit - removed picture with serial numbers

And yes wifi disconnected to playbar. 

And yes wifi disconnected to playbar. 

 

You cannot disable WiFi on a Sonos soundbar if you have a Sub/surrounds.  You need WiFi on for the private 5GHz connection to the Sub/surrounds. 

As already intimated, the Playbar uses a wifi signal to communicate to the Sub and surrounds so you need to turn it’s wifi back on. 
I also note your Playbar status is “not connected” in your screenshot. Do you know the reason for that? If not I’d suggest a router reboot with all Sonos speakers turned off. When router and wifi is fully restarted power the Playbar and get it connected. Then power other devices one at a time. 
If all is then good it may be worth allocating static ip addresses for the Sonos devices. 

Thanks.  The playbar is connected using an optical cable and is working

So are the rear speakers (Sonos ones).  It is only the sub that doesn’t play

Are the One’s also cable connnected?

So what happens if you would turn wifi on your Playbar?

Rear speakers not wired nor is the sub

would rather not play around with the playbar. It is the one thing that keeps working and I was told not to play with it. 
 

I wonder whether the Sub has failed? Have you generated a diagnostics and spoken to Sonos support?

The optical connector has nothing to do with the communication to Sub/surrounds. Have you re-enabled the wifi? 

Yes

Is the Sub also wifi-enabled?

 Once you’ve enabled WiFi on both PLAYBAR and SUB, rebooting both might be the magic bullet.