What to replace Sonos with

1/ Remove the Bridge unless/until you can test its wall-wart power supply. Substitute another Sonos device for now. The PSU has a risk of failing with age. The voltage drops, and the Bridge's connectivity becomes intermittent. A healthy PSU puts out a steady 5.1V.

2/ Remove Sonos' dependency on the EoP (Ethernet over Powerline), even for the controllers. It's very variable, and any attempt to use it across the two consumer units is really asking for trouble.

I am not connected to SonosNet

That's inconsistent with the fact that a Bridge is deployed. If you've ever been persuaded to configure WiFi details into the system then:

3/ Remove the WiFi credentials via the 'reset' button at Advanced Settings/Wireless Setup.

Just read - Android. Have you tried connecting them to SonosNet rather than WiFi?

Thanks for helpful input, John. Support suggested I didn't do that, but have just done so, Will report Back. Reading their info suggests that I should tell my phone to forget the router's wifi. Is that best? I don't use the phone for streaming - just whatsapp, email, news, casual searching.
thanks

At least for the purposes of experiment, and given your use of phone, I'd suggest forgetting the home wifi to ensure phone sticks to SonosNet.

I was going to suggest the same as @ratty and propose you get the Play:1 from top floor and wire it in place of the Bridge. Longer term a Boost might be worth it. Locate the P:1 at least a metre from router if possible.

Do you know which channel your router is using? There are plenty of free wifi scanner apps in the Google Play Store and they can provide useful, though not comprehensive, information.

Note: after replacing Bridge as wired device, give things a couple of minutes to reconfigure before you think your system has disappeared!

After all the above, go to http://IP_address_of_Play1:1400/support/review (get the IP from About My Sonos System). Open Network Matrix and post a screenshot.

I'd also like to see confirmation of what the EoP is being used for. It can be a silver bullet, but at other times it can be hugely frustrating. Basically if one doesn't have a management app/console that reveals the state of the EoP connections one has only a rough idea about what it's doing.

1/ Remove the Bridge unless/until you can test its wall-wart power supply. Substitute another Sonos device for now. The PSU has a risk of failing with age. The voltage drops, and the Bridge's connectivity becomes intermittent. A healthy PSU puts out a steady 5.1V.

My bridge power supply is showing 6.7V.

2/ Remove Sonos' dependency on the EoP (Ethernet over Powerline), even for the controllers. It's very variable, and any attempt to use it across the two consumer units is really asking for trouble.

The powerlines are separated because of the problems of two consumer units. Different hard-wires from router to different powerlines, with separate pairing to keep them apart. The Diskstation is hard-wired (via a switch) to the router. So I don't think I'm depending on powerline except to get catchup TV to the Humax (which mostly works flawlessy). Correct me if I'm wrong, but I don't think the Sonos is at all dependent on the powerlines.[/quote]

I am not connected to SonosNet

That's inconsistent with the fact that a Bridge is deployed. If you've ever been persuaded to configure WiFi details into the system then:

3/ Remove the WiFi credentials via the 'reset' button at Advanced Settings/Wireless Setup.[/quote]

No credentials there - I took that out previously at Support's suggestion. I get the "Set up Sonos on your Wi-Fi" screen, "Let's get Sonos running on your wireless network"

thanks all

I would still swap out the Bridge as it uses SonosNet 1.0 not 2.0. Give the SonosNet phone connection a try. A screenshot of matrix, as suggested by @ratty, would definitely be worth it.

My bridge power supply is showing 6.7V. Either it or your meter is faulty.

Correct me if I'm wrong, but I don't think the Sonos is at all dependent on the powerlines.

If the Bridge is/was the sole wired device then the Sonos units won't depend on EoP to interconnect. However a controller in a device using an EoP-based WiFi could encounter problems.

Initial results seem to be positive. Just tried grouping - no problem.
Just tried playing from diskstation - no problem

thanks all, let you know tomorrow when I'm back online. Out now till 10pm.