Dimmer switch

[greenrook]

Hello All. I've just replaced the living room rotary dimmer switch, as the old switch would turn the lights on and off but wouldn't dim them. The new switch appears pretty much identical, I wired it exactly like the old one and it works fine, except when the lights are turned completely off, there remains a very faint glow from the bulbs. Is it simply a wonky switch or have I done something stupid? I don't know if it's significant, but the old dimmer stopped working properly immediately after one of the bulbs in the chandelier thingy exploded.
Any help gratefully received...Greenrook

[buildersmate]

So the new one is just a dimmer, and not an on/off switch as well?
Are you sure you don't have to depress the button to latch the switch on/off by each successive push? - I've seen a few like that.

[greenrook]

Hello BM, I should have expressed the situation better - the switch is also an on/off switch, you turn the knob clockwise and the lights click on then grow brighter as the knob is turned further clockwise. Turning the knob anticlockwise progressively dims the lights, then they go out. The old switch didn't have a push/pull function, though I've seen those too, and neither does the new one. Having said all that, and looking at the pack it came in, I see it's described as a 1 gang 1-way rotary 250 watt dimmer switch. No mention of an on/off facility. I asked for a dimmer switch, and perhaps they've sold me exactly that? I did take the old unit in to show them, but I don't think the bloke on the counter was an electrician necessarily.

[buildersmate]

Well I'm happy to be told otherwise - but I thought that dimmer switches that switched right off either did so via a 'click' (switch going off) at the end of the rotary travel anticlockwise, or via the push on / push off arrangement discussed above. The reason they need this is because the rotary knob drives a variable resistor that controls electronic circuitry that drives a triac. Although turning the knob anticlockwise reduces the power through the triac to near zero, it does need to be electrically disconnected to be 'off'.
I think you've got a dimmer which is intended to be switched on/off from a separate external switch.

[scotman]

Did this come in a box with a wiring instruction sheet? That should say whether it includes a switch.

[greenrook]

Yes BM, the click occurred at the end of the rotary travel with the old switch, to totally extinguish the lights. There is no alternative on/off switch anywhere. The click occurs with this new switch too, but the lights remain just barely illuminated. Sounds like I should have asked them for a dimmer switch which incorporates an 'on/off' function.
And no Scotman, the rather sketchy fitting instructions don't identify the unit as one thing or t'other. I thank you gentlemen for your help, I believe I now know what I must do.

[greenrook]

Took the switch unit back to the electricals shop - they confirmed it was simply a duff switch, and replaced it. I fitted it and all is well. Thank you both for your suggestions

[buildersmate]

Ah well - glad we all sussed it in the end.