Sonos system won't connect to my router.

​@Karis, The Sonos Bridge may be defective, please disconnect it. You can wire one of your other Sonos products instead (surround speakers are not suitable for this!), or you can connect the system to your router's Wi-Fi.

Remove a Bridge from your Sonos S1 system | Sonos

Try to take all Sonos components off the power (about 5min) in the meantime restart the router. When it's back online, try your Sonos components little by little, if not already on this way. Do you only have one router or also APs?

Is it likely the old Sonos Bridge has become defective, it’s always worked faultlessly, so how can I tell? I understand that a Sonos Bridge has not been required for some years but I’ve stuck with it, looking at the link am I correct in saying it’s still possible to connect older Sonos speakers directly to the router via wi-fi? I only have 1 EE router.

It’s hard to ‘tell’, the symptom is your system no longer connects to it, or exhibits difficult to trace network connections.  As suggested by ​@Smilja , you’re better off connecting your Sonos devices to your WiFi. All Sonos devices, assuming they’ve been updated in the last 19 years or more, will do so, they no longer ‘need’ the BRIDGE to connect. Whether they’re S1 or S2 systems. See the information in the wired and wireless modes FAQ, and other related FAQs

At this point assume that the ancient BRIDGE has a (potentially intermittent) hardware issue, often the power supply. 3rd party replacement power supplies are available, but it’s usually not worth the bother. Eliminating BRIDGE, as described above, is a better long-term solution. A SONOS BOOST can directly replace BRIDGE, but BOOST is also an obsolete product and not worth the bother.

If you can measure Voltage, a functional BRIDGE power supply will put out slightly over 5.0V. Less than this you’ll begin to have difficult to describe intermittent issues. Again, it’s no longer worth fussing with.

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When BRIDGE was introduced it was revolutionary. Mesh networking was not yet easily available on the consumer market.

SONOS players had been mesh since product inception in 2005, but it was a private mesh requiring at least one SONOS product to use a wired network connection. BRIDGE was introduced to inexpensively provide this connection when it was physically inconvenient to wire a ZonePlayer to the network. BRIDGE could also be used as a wireless mesh point. As SONOS began to acquire significant market penetration, competition would trash SONOS’s claim of being “wireless” because of this one required network connection. Never mind that the competition struggled to support more than a couple wireless players while a SONOS system could support 32 players as long as long as one or more was wired. For a while SONOS attempted to deal with this trashing by including a free BRIDGE with a system purchase. But it was still too easy for competitors to trash SONOS as not being “wireless”. Eventually, SONOS relented and allowed players to use WiFi or the private mesh and the competition’s “trash” claims evaporated overnight. It’s a giggle that in the background many of these competing companies that were trashing SONOS quietly started licensing SONOS’s wireless patents and can now reliably support more than a couple players too.

Anyway, consumer grade WiFi has matured since 2005. That era SONOS networking would be classified as WiFi4, but WiFi6 and WiFi7 are now very common on the current consumer market and public mesh is widely available. There is no point for SONOS to continue supporting its private mesh. Currently manufactured SONOS units do not support the private mesh (SonosNet), but legacy units can still use their SonosNet connections.

Thanks to all for responses, I’ll try some of the suggestions & post back.