I have two dimmer switches that have started malfunctioning. They are in the same box with two other standard switches. Each controls a set of three small flood lights. There is no other way to control these floods except with the dimmer switch. They were working fine last week. Now, when I slide the dimmer, it sometimes works and sometimes doesn't. I know it isn't a circuit breaker problem since the other switches are on it as well and they work. These were installed about 6 years ago. I will need to call an electrician to fix this but would like to have an idea, if possible, of what the problem could be.

  • When it "sometimes doesn't" work, do the lights come on at all?
    – K.A.Monica
    Jan 5, 2014 at 2:48
  • 4
    In my experience, dimmers seem to fail relatively frequently compared to switches.
    – Steven
    Jan 5, 2014 at 2:51
  • 1
    I don’t know which type of construction you have, but if the sliding part is attached to some variable resistor, that may simply be dirty and/or worn out. It will probably be more economical to get new ones than to pay an electrician to take one apart and clean this place, though – even if that would be slightly cheaper, the problem will resurface, probably sooner than with a new one. Jan 5, 2014 at 14:35
  • 5
    Dimmers have maximum ratings (usually 300 watts or 600 watts). If you exceed the max, they may burn out. Also if they are mounted next to each other, part of the heat sink face plate is usually trimmed off, reducing their wattage max.
    – bib
    Jan 5, 2014 at 21:05
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    Thanks for your replies. I don't trust myself to do anything electrical. I will call my electrician to check it out and replace them.
    – user19119
    Jan 9, 2014 at 19:03

2 Answers 2


Sounds like a simple case of a bad switch.

Note: a squirt of WD-40 into the right place in the sliding mechanism can help, or even fix the problem at least temporarily by lubricating the internal sliding electrical contacts. But getting the location right requires experience, and if you have to bring out an electrician anyway, they'll prefer to replace.

Do this with the power off by the way. And it's far better to take it apart and lubricate, compared to the squirt and hope method.

Consider upgrading to a dimmer model with a remote control, CFL compatibility, or other features.

  • 4
    WD-40 is flammable. Spraying it into a light switch is probably not a good idea.
    – nobody
    Jun 9, 2014 at 20:00
  • With the power OFF.
    – Bryce
    Jun 11, 2014 at 3:36
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    WD-40 is bad for plastic, use contact cleaner if you must.
    – Mazura
    Aug 19, 2014 at 1:46
  • True, I have wrecked dot-matrix printers by wetting dried-out ribbons with WD-40. Mar 11, 2016 at 21:15

Your dimmer was probably damaged by excessive heat and maybe more load than it is rated for. Solution:replace bad dimmer with one that is rated at or above the amount of watts you are controlling with it if one dimmer is a 3 way you may be able to put that one on the other end and a regular 3 way switch at that box. Otherwise you may be able to change your lamps to dimmable led s that will reduce the load and also the heat. But still replace the dimmer they are not repairable.

  • Can you point to the section in the National Electrical Code that prohibits multiple dimmers in a single box?
    – Tester101
    Aug 8, 2014 at 15:40
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    I'm not aware of anything prohibiting it. Most dimmers have heat sink fins that can be snapped off for higher density installs, however every fin that is snapped off reduces the wattage rating of the dimmer per the manufactures specs. So it really has more to do with load on the dimmers then the number of dimmers in a box.
    – Steven
    Aug 8, 2014 at 17:34
  • Sorry I knew I had read that somewhere it must have been in the manufacturer's instructions for a dimmer that I have used in the past . one that I was just looking at describes a reduction in wattage per number of dimmers ganged.
    – user24125
    Aug 9, 2014 at 0:45
  • No sense in asking for a code reference because it does not exist. As Steven says, it is clearly explained in the instructions how to break off the fins if dimmers are to be ganged. Aug 10, 2014 at 12:08

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