@woozle thank you. How irritating! I used to have a very sensible range extender which worked well swapping between the router and the extender. And now I have something much more sophisticated that...

And yes, you're right, the same password works. Should I worry that my iPhone says that the range extender is 'low security'? Thanks

@woozle Thank you. The router is a SR203 - a Sky one. No hardware or other numbers. The extender is RE550 (UK) ver 1.0 Thanks.

I plugged my AC 1900 range extender in, pressed the buttons on both it and the router and hoped for the best. I can see my router and connect to it. There is a second WIFI thing which is router_EXT...