I have bought a house which has a single switch at the bottom of the staircase and a double switch at the top on the landing. On of the switches in the landing switch operates the landing lights (there are two bulbs) the other a light in a bedroom.(Oddly, there is no switch in the bedroom itself)
When I switch on the light in the stairs then I can switch the landing lights on and off using the switch upstairs. However when the stairs switch is off and I turn on the switch upstairs nothing happens. The switches have common, L1 and L2 and the wires are red and black. The earth is connected to the inside of the back box.
I have tried different combinations but can't seem to find one which will allow me to turn the landing lights on and off when the stairs switch is off.
Any help much appreciated.