He's already said a phone works in the master socket...
I see now.
If it was a different phone, then it may be that her phone is faulty.
Thanks for sharing the video. In my mother-in-law's case, the extension is not wired into the back of the faceplate, but terminates in a small square plug which is inserted into a small gizmo with a flat plug which in turn is inserted into the faceplate (so when the extension is in place there is no socket for a phone, but that's not a problem).
There is definitely a good signal here, but not at the other end of the extension. Since I have neither skills nor testing tools, I guess I'm going to have to get an engineer in. Thanks everyone!
Ah I see, ye olde telephone extension kit! Then I expect it should indeed be the blue/whites that are connected to 2 & 5 in the extension socket. Easy enough to try as you'll do no harm or a complete replacement kit (with instructions!) would be less than a tenner.
You hopefully realise that extension sockets and wiring are not Openreach or BT ( presumably it’s BT that are the service provider ) responsibility, so calling OR out( via BT ) could result in charges for the visit.
FWIW , often , if extension wiring has been run under door thresholds, rather than surface wiring on skirting etc, then the foot traffic over time damages the cable resulting in it breaking…as far a the wiring it ( obviously) doesn’t matter what colour wires used between the main and extension sockets are used as long as it’s the same at both ends
If an openreach engineer does come out (doubt it as line woukd test OK) They would only test up to the main socket, they would not work on any sockets after the main one. You would also get a bill due to no fault on line, customers own wiring.
Thanks again for all the advice. In the end I decided to fix it the hard way by lifting the carpets and replacing the wiring (wiring behind the faceplate of the master socket). This did the trick.