Well in a twist of irony, posting on this forum I'm asked for the model type and it isn't even listed!
For the rest of you reading this it is TL-WA855RE
Right what seems to be the problem then... Incorrect password! I can see that the forum is littered with the same problem and most users are left with little help on this topic.
I brought this to extend one of my wifi networks. I put the extender within range of the router and sure enough I got a blue light suggesting all was good. I connected to the range extender and was prompted for a password. I tried the password that was already set with the SSID for the router and it came back as incorrect... Oh! perhaps I typed it in wrong... Anyway after many attempts I gave up.
Last week I decided perhaps a better way would be to hardwire the extender to the router via cat5e. Did that and reset the extender. Sure enough a blue light and I was also able to connect to the extender and was prompted for the password. Again incorrect password.
Clearly this isn't a very good piece of network equipment.
Before i take it back to the shop for a refund, I'll ask here if anyone has solved the mystery of the password.
I'm no stranger to IT, previously I worked for Unisys as a network engineer for all of the major banks in the UK. If this has baffled me, the home user will be completely lost with one of these.