There's an RSJ between the router (back bedroom) & main living room at the front which restricts connectivity.
I got a plug-in Belkin booster the other day, managed to get it speaking to the router using my iPhone 5s (yay me!) & since then my phone & DS2's laptop & Samsung phone have connected fine most of the time (have to reboot booster occasionally).
DD2 visited today and her iPhone (also 5s I think) just would not work, despite showing a full connected signal???
We tried shutting down her wifi connection & logging in again, but nothing worked until I switched the booster off.