Changing Thomson 585v7 router from talktalk to plusnet

[#1]

I have been with plusnet for years - with a Thomson 585v7 router which has been 100% OK.
I thought I would buy a spare one off ebay (£3, identical model) just so I had a spare. However, it has been used with Talktalk and despite doing a factory reset both via the reset button on the back and on the thomson website, it refuses to want to connect to anything other than Talktalk, which obviously I cannot do as I have no account with them.
I have tried logging into the router on the Thomson site (192.168.1.254) and I have tried all variants of the admin/ password that are known with this model. Depending when it was made you use either 'admin' or 'Administrator' as the user name and either the SN of the device as the password or no password at all, all according to guidance on the plusnet site. The password is the router serial number (SN) on the base - starts with CP (numbers and upper case letters).
Plusnet advised by phone that the firmware in this 585v7 router may need to be 'reflashed' to get rid of talktalk and allow it to connect to anyone else.
So how do I do this?

[#2]

I guess if the router is the same but only the firmware is different then you should be able to just get the normal thomson firmware and flash it.
If plusnet have firmware to download then i would download the one needed and try to flash the router with it. Don't see there being any problems if the hardware is the same.

[#3]

Is this the procedure I need?
http://community.plus.net/library/hardware/how-to-upgradedowngrade-the-firmware-on-the-thomson-585v7...

[#4]

yeah thats looks right to me.

[#5]

Don't know if it applies, but there is a suggestion here from 2009 that some of the routers are locked and need some hardware to unlock them. The reference is to an O2 version.

[#6]

Brilliant article (cited above) and very helpful. Problem solved.
Summary: I bought a £3 585v7 router off ebay as a spare (just in case) but it was programmed to work only with TalkTalk, I followed the instructions on here
http://community.plus.net/library/hardware/how-to-upgradedowngrade-the-firmware-on-the-thomson-585v7...
and now it is working on Plusnet with 8.2.6.5 firmware.
Only point to watch is that some devices apparently have Administrator as a username, some have admin. admin (all lower case) worked for me after the firmware upgrade. The router password is the CP number (S/N) on the base of the router - note all upper case letters in this. Then just tell it your plusnet user name and password and it connects to internet in no time.
Thank you to the authors of the above support article!!
I can now upgrade the firmware on my original router too.

[#7]

Good posts guys, I'm sure this will be helpful to anyone else wanting to do the same.
Adam