I have now cabled into the TL-WR940N the printer and now works via ethernet cable.
Weird.
Have two cabled devices - i.e. desktop & printer connected via the TL-WR940N but I am unable to access the TL-WR940N (192.168.0.1 )via the desktop PC.
I also unable to connect the printer in WIFI mode

You would better contact tplink support if your devices are latest firmware from them official website

Many thanks.
I have emailed them earlier today with details as described above.
Haven't heard anything yet.
Will call if no reply
The problem has been very time consuming but I am managing with router 'acting more like a switch'.
I purchased the item last November so well within any warranty.

Thanks again.

What's your network map? Is it EE main router --(Ethernet cable)--TL-PA4010---(electric wire)---TL-PA4010---TL-WR940N----PC ?
If you want the TL-WR940N to work as a switch, you should disable the DHCP server of the TL-WR940N, and it's better to change its LAN IP address to the same subnet as your main router.
Like if your main router's IP address is 192.168.1.1, you should change the IP of the TL-WR940N to 192.168.1.X (1

Enson - many thanks.

Have had a response from TP-LInk now - many questions but haven't found an answer.
The Network Map is as you state with the EE main router in the lounge and the TP router in a bedroom / study

The Desktop (in the study) is ethernet connected into the TP router. - It can access the Internet but can not access 192.168.0.1 (the TP Router) but can access the EE Router 192.168.1.1
The WIFI light is now on and I have reconnected my printer (in the study) via the TP WIFI and works
I have a LAPTOP (old box with LINUX Mint) normally used for watching TV which has previously been connected via the TP router using WIFI.
I can connect to both routers from this laptop - i.1. 192.168.0.1. & 1.1 but (at the moment) this box refuses to connect to internet (I don't understand this one bit).
I now have my printer working via the TP WIFI connection (i.e. it will print from the desktop using the WIFI)

All this 'went wrong' after 're pair' ing the TP EXtenders - but not aware how that could be responsible.

Just a mess at the moment and have spend several hours.
PS The internet light does not illuminate on the TP Router

Sort of got something that partially works but no laptop access to the internet !

looks like I solved the problem. Guess my fault - 'redid' everything - cabling rebooting etc and seems to be back 'as was'.
TP-Link provided help - i.e. 're-do' everything