[Jim]

probably because i've not understood a word of the last 3 posts you've put up

[dave]

Shouldn't you be reinstalling windows right now?

[Jim]

er no. IIRC its sounds to me like you've gone a ridiculous way around trying to make up for the fact you've got a shit router when the solution was a simple and obvious one, IE switch your virgin router onto modem mode and buy a decent router

[dave]

Decent routers looked to be similar money to the power line kit, would still have two supporting walls to get through, so front room would still have been a weak spot.

[mr__j5]

Sounds like everything that you did was perfectly sane.

No idea why the chromecast wouldn't work but I don't know much about them.

Certainly multiple access points with the same SSID, same encryption settings and same password should work fine.
Sometimes it might take a bit longer than you'd expect for a device to switch from 1 access point to another if you wander around the house, but otherwise should be pretty seamless.

[dave]

Cheers, I might try disabling the wifi on the router to make sure the Chromecast is connecting via the powerline.

[dontfollowme]

 Dave not sure if it helps but Chromecast has to be set up from a wireless device. My wired PC can cast to my TV but the initial set up had to be done via my laptop connecting wirelessly.

[dave]

Yeah I already set it up the first time round fine via iPad. Trying the same again just on a new instance of the old ssid.

[slackline]

You could try the Factory Data Reset.

[slackline]

If a Factory Data Reset doesn't work you could try soliciting assistance in the Official Google Chromecast Product Forum or perhaps on /r/Chromecast.

Not had this problem myself so can't offer any insight and as mr__j5 says you've done the sane/logical things already.