Once you’ve reset all of the speakers and the controller, you won’t be bothered about the previous owner.

On turning the screw. Some folks (including me) like to use thread locking compound on screws like that. If they picked up the wrong compound, brittle, not sticky you could need an impact driver to hit it with enough force to get it free, might destroy the socket too, depending on the strength of the locking compound. Extra bad choices could also require heating the screw which would ruin the socket.

I like LockTite Blue for things like this, strong enough to keep the screws tight but only a bit more force needed to remove them.

Worst case try combining locking pliers on the head and your driver inside, then apply pressure to both, then tap the locking pliers with a brass mallet to see if you can fracture the bond.

ALI_101,

Likely you can press the Join button using the eraser end of a pencil — without dismounting the speaker. But, you’ll need to use my circuit breaker trick or trace the power cord to its outlet.

Thanks everyone for your support. 

As i first port of call i will try to cut the power to the downstairs speaker via the curcuit breaker. There must be 30 switches on our curcuit board, once i can figure out which is for this speaker i'll get onto it.

You’ll need an assistant to throw the breaker because there will be a timeout if you attempt to run back to the speaker and press the button.

So i finally managed to cut the power to the house and factory reset both speakers. On th3 Sonos app i choose to set up a new system It quickly finds both Sonos One speakers. It then plays a chime from the speaker which means the app in my phone recognises it. It then asks me to input the WIFI password. When i do, it gives an error message saying to recheck the password is correct????? The password is 100% correct. After 3 attempts to put in the corr3ct WIFI password, it comes up with a screen on 'adjusting your router settings'. !!!!! 

I have a normal modern router that supports both 2.4 and 5ghz, model Archer AX73 AX5400 Wi-Fi 6 router.

I am no good at logging into the router and adjusting settings etc. If this is neccessary i have no clue how to do this, though i cannot understand why it would be neccessary  the wifi works perfectly well, every other device we have ever had connects to it without any issue.

Any ideas what can possibly be causing the problem now? I'm at my wits end with these speakers.

Sonos speakers can get confused by 5Ghz networks using the same name as 2.4Ghz networks. The fault message does not help. You could try temporarily disabling the 5Ghz network.

You nailed it!

I changed from 5g wifi to 2.4g wifi and it now works. Both speakers are now up and running, finally. Thank you for your support!

What a pulava it has been. 10 months of trial and tribulation just to get a couple of speakers set up. Sonos really need to make the set up process much simpler and user friendly. Not everone is a tech extraordinaire.