Dimmer light won't fully illuminate

20 Feb 2017
Reaction score
United Kingdom

We have an open-plan living area. There are two dimmer switches that operate the kitchen lights: a 3 way dimmer and a 2 way dimmer.

Recently we have noticed that when the kitchen lights are fully turned on they are only half as bright as they used to be, and noticeably less bright than other lighting zones..

We have ensured the switches on both dimmer panels are turned on rotated, so this is not the issue.

We have also noticed that when rotating the dimmer switch in the Kitchen zone, the light disappears halfway through the rotation, unlike the other zone where the dimming happens throughout the dimmer rotation. This happens on both the 3 way and 2 way dimmer panels.

Does this sound like a dimmer switch needs to be replaced? If so, how would I determine if it is the 3 way or the 2 way that is failing?

Sponsored Links
Is it safe to assume that nobody has done any work on any part of the lighting circuit between the time when all was well and now?
Sponsored Links
I am trying to work out what you have, a two way switch will divert power to either of two outputs, and can be used to allow full control from two switches, a three way switch will divert power to one of three outputs like signs saying Out, Please knock, and Wait, would likely be rotary and can't really see how they would be used in a house?

So I am trying to guess what you mean, with dimmer switches the two way system is not the same as with on/off switches, you have master and slave switches and the slave in essence tells the master switch what to do, it has a sensing wire, so still three wires plus earth used, and it is like to like, just like on/off switching, but it is a case of following manufacturers instructions to the letter, some dimmers will work with an on/off type switch, normally a push/pull on/off on dimmer and turn to adjust light.

however putting two of the dimmers designed to work with a on/off two way switch to work with each other will not work, the dimmers have to be master and slave to have two dimming switches on the same light. I am guessing you have two dimming switches on the same light which are not designed to work together?

When you have three on/off switches to work one light it is still called two way switching, the centre switch is called an intermediate switch it is in fact a change over switch. With dimming switches you can often have more than one slave.

With LED lamps it get more complex, the LED bulb is designed to pass a low amount of current without lighting, however the amount is not standardised unlike 5 - 20 mA devices used in industry, so it is a bit hit and miss what works, some LED bulbs are designed to compensate for volt drop, these will also likely compensate for any dimmer switch action, it is possible to dim lights today many different ways, including having all the dimmer unit built into the bulb, you can get a bulb designed so you can dim it with your phone, and it has a permanent supply.

So until we know exactly what you have, can't really answer the question. When you say a three way switch what do you mean? is it a three gang switch, or an intermediate switch? I know the names given can be confusing I understand that, but to answer we need to know what you have.
So just to be 100% - you have not changed any switches, dimmers or ceiling light fixtures?

Can you describe in more detail what the current setup is? How many switches or dimmers on each plate etc. Ideally upload photos.
The best i can guess is that you have a 3 gang plate and a 2 gang plate, some of which might be 2 way but as you mention 'rotating' and 'both panels' it's a bit hard to visualise your current setup.

You may already know (But I can't understand the problem unless you've described it wrong) 2 way/3 way etc refers to the number of switches controlling a specific light (or group of that are always on/off/dimmed at the same time). 2 gang/3 gang refers to the number of switches/dimmers next to each other, each of which controls a different light (or lights).
Sorry, I have got the terms wrong. So back to basics -
  • We have 18 downlight / spotlights (with GU5.3 Halogen Bulb 35w bulbs)
  • These are in 3 lighting zones (living area, dining area, and kitchen area).
  • In the living area, there is a triple dimmer switch - a dimmer knob for each lighting zone.
  • In the kitchen area, there is double dimmer switch - a dimmer knob for just the kitchen and dining area
  • No LEDs (we would love to have LEDs, but apparently we would need to change each of the downlights as the transformers are within the downlights)
  • The kitchen area has the problem with the area not being lit fully any longer. There are 6 lights in that zone.
Hope that makes a bit more sense.
So you have dimmers at both switches.

Are they the Master/ Slave type? Or are they normal dimmers? If they are ordinary dimmers, you should only have them at one end or the other but not both.

If they are Master/ Slave, then, assuming no alterations have been done to the lighting, one of the switches may be faulty.

To determine your switch type, we would need pictures of the inside of each switch.

Does the lounge switch set up have another switch or is there just the one (dimmer) for the lounge lights?
Yes, that makes a lot more sense, thank you for explaining.

I think securespark above is thinking along the same lines as myself. As he has said, multiple dimmers on a single circuit will never work sensibly, unless they are of the master/slave type. Are all the dimmers single turn (ie. a physical knob that you rotate until it hits the stop) Previously did you have to rush between switches cursing because the other dimmer was left low?
Thanks for your help - appreciated.

We are not sure about master/slave. They are new terms for us.

I can get photos of the inside of them this weekend.

There are no other switches for the lounge lights. The lounge lights are only operated by one of the knobs in the triple dimmer.

Yes, all the dimmers are single turn with a physical knob that rotate until the knob stops. Pushing the knob in turns them completely on and off also.

We still do have to run between the dimmers as one always seems to be left too low. With kids turning on the lights, it means this is a constant annoyance.

I have no idea why it was set up this way. We never dim the lights in kitchen, nor the dining area. We only ever dim the lounge area.
If you only ever dim the lounge, then replace the 2G dimmer switch operating the kitchen and diner with a normal 2G rocker switch.
Sounds like you have standard dimmer switches if the 3rd gang works fine. A simple check inside the faceplate will reveal all, and the fix would be to swap one end for plain 2-way switches if they turn out not to be master/slave dimmers.
I have no idea why it was set up this way.
I can tell you exactly why.

It's because it was done by somebody who didn't know how to do it properly, didn't bother to read the instructions which came with the switches, and didn't see why his ignorance and laziness should be reasons why he ought not to even have thought about doing DIY electrical work.
I can tell you exactly why.

It's because it was done by somebody who didn't know how to do it properly, didn't bother to read the instructions which came with the switches, and didn't see why his ignorance and laziness should be reasons why he ought not to even have thought about doing DIY electrical work.

Yep. The guy how owned the place before us was a builder, and I would bet that he did the electrics.

We will check inside the switches to get a photo for you to confirm the master/slave.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links