having a few difficulties with our upstaires light .
one night switched the light on for upstairs and went up staires and went to turn it off and the the light stayed on . so went down staires and tried that switch and still wouldn't go off . the light just flicks as you flick the switch but stays on .
The original fault could have been a switch- the strappers run between the two switches, one strapper is always live- they take it in turns as each switch is operated - if both are live (faulty switch, damaged cable, or incorrectly wired switch) then it would not be possible to switch off a two way lighting circuit
Either original fault has to be switch or wiring the latter means a re-wire so I would pray it is switch.
I would get a block connector and after noting original wiring put each wire of one switch into separate terminals and seeing if light goes off if it does then likely to be switch wiring. I would guess one switch with 5 wires and other with three wires on one with 5 wires I would test pair of wires to see if these are switching on and off i.e. com to L1 if so then next is to wire two way which means moving pair to L1 and L2 and wiring both switches with three core colour to colour i.e. if blue goes to com on one switch it also goes to com on other switch.
Look at my diagrams to see how it works. We do not wire the same as taught at school as this requires a connector block in first switch but method I have shown uses L1 and L2 in first switch to connect to two cables together.