In my sitting room I have two lights on the ceiling, each with three bulbs in. On the wall is a two button dimmer switch (press each knob to turn on lights, rotate knobs to dim)

A while ago the dimmer part stopped working, so today I bought a new dimmer switch - looks exactly the same;



Unscrewed the wall plate and inside were 4 wires - 2 red, 2 black (with red sleeve). The red wires went into L1 (one into L1 on each black plastic bit) and the black wires went into the what looks to be marked as ground (?)

Well after swapping the swithc over I turned the lighting ring back on and one of the lights now flickers, and although the dimmer works, it's so dim at "full bright" it's useless, and the other one doesn't flicker, is just as dim, and buzzes a bit from the switch. So I swapped the switch over again to the original, which works at proper brightness, no flickering, but the dimmer is broken (as before)

Any idea's whats wrong?