Help please, double light switch rewiring

Just bought a new house and all the old sockets/switches were disgusting so decided to change them. All the sockets and single light switches were fine however i was stumped by the double light switch any help please?
Old one currently wired in and only one light working
New double switch

Thanks

Have a look in the backbox - does the black, yellow and blue come from one cable or two separate cables?

Same with the two reds. Looks like whoever fitted that switch has got themselves confused, somehow, and put the two lives together.

Is it the switch on the left of the first picture (so on the right when it's on the wall) that operates the light that works? And only when another switch somewhere else is in a certain position?

The old switch appears to be wired strangely, that may be why only one switch is working. I would try to resolve that before tackling the switch change.

Note the diagonal line moulded into the plastic on the back of the old switch. That denotes the division between the two switch units. The old switch has two sets of three contacts arranged in a triangle, one upside down, t'other right way up.

In general, all three wires of the 2-way switch cable (3 core & E) will connect to the terminals on one side of the moulded line, and the cable colours to terminal designations will be the same as the other 2 way switch for that light.

Be extra careful about proving all the wiring is dead before working on it - there may be live wires from two different lighting circuits present in that back box, and if they have been crossed up some parts may be live when you don't expect them to be.


It's possible whoever changed the switches before made the classic mistake of assuming the top and bottom rows of terminals denoted the division between the two switches, leading to the problems you are trying to correct.

Make plenty of notes about what is connected where on both this switch and the other 2 -way switch before taking anything apart, so at least you can get everything back to your starting point if things go awry.