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We had 2 dimmer switches that had stopped working (lights were on 100% regardless of how turned the dimmer switch was.

I checked the back and went out and bought 2 new ones, turned the electricity off and swapped them over.

They both control 4 lights and they both work ok, but on one it buzzes constantly. Is this a sign of a faulty dimmer switch or is there something else going on?

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  • Are you sure it's the dimmer and not the bulbs?
    – ChiefTwoPencils
    Jan 19, 2015 at 9:54
  • Buzzing? Yes it's the dimmer switch buzzing.
    – user4428391
    Jan 19, 2015 at 13:05
  • Attempt to replace the bulbs with old incandescent ones first. I had this problem and it was simply that LEDs aren't dimmable the switch buzzing was really irritating.
    – James
    Jun 26, 2015 at 13:44

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This can also be a sign that you bought a dimmer that is designed for incandescent bulbs, but you have it controlling CFL or LED bulbs. This can absolutely make it buzz. If the dimmer was not explicitly for CFL and LED bulbs and those are what you are running, then you need to get new dimmers that are explicitly for those bulbs.

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Most likely a faulty dimmer if one buzzes and the other doesn't. Are the bulbs on both circuits the same type? Make sure the bulbs are designed to be dimable. (not CFL's)

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Yes, a faulty dimmer. But only faulty by manufacture, not operation: certain components within the dimmer circuit will vibrate, at 60Hz and 120Hz (or 50/100Hz if that's your mains frequency). Because of this, manufacturers glue everything down, a process called 'potting', to the point where no components could ever be removed. Nobody's going to bother trying to fix one, so it doesn't matter. However, in your case they've been frugal with the glue, or just careless. Ultimately the dimmer isn't going to break or do any damage (except to your sanity with it's incessant buzzing). Replace it if you can, as the buzz is likely to worsen, but there's no risk if you continue using it.

You get the same from switch-mode power supplies, like laptop chargers or walls warts. Put your ear to them when they're on and you'll hear a very high pitched whine. The cheaper, the louder!

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  • Thanks! So is it safe to say that the buzzing wouldn't be caused by me buying the wrong switch? I mean, I checked one switch and went out and bought two of those, but then I had a thought that maybe they were both different and that is what was causing one to buzz? Is a house usually the same throughout?
    – user4428391
    Jan 26, 2015 at 14:35
  • Provided that the two new switches are identical, try swapping them over. If the buzzing switch still buzzes in its new location and the non-buzzing one still doesn't buzz you know for definite that the switch itself is faulty. However, I didn't take into consideration what type of bulbs you're using with each one, what their power rating is and how many there are. I ignored these points in my main answer because you said you were replacing broken dimmers with new ones, therefore I assume the bulbs themselves are compatible with dimmers. Swap the switches around first, and we'll go from there.
    – CharlieHanson
    Jan 26, 2015 at 14:52
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I had this problem. My house is a bit older and I started replacing bulbs in the basement as they burnt out.

I pulled out incandescent bulbs and replaced them with LED bulbs.

The dimmer started buzzing and I though "eh, its an old switch its probably going bad."

I started with the dimmer switch, replaced it, still had the problem, replaced it a second time...still no luck.

Turns out the problem was simply that I had been replacing the incandescent bulbs with LED bulbs. Standard LED bulbs are NOT DIMMABLE.

(You can buy dimmable LED bulbs, but in that case I would recommend updating the switch anyway as the power load is different)

Always try the cheap fix first. I ended up just taking the dimmer out and putting a standard switch in place.

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