# Light switch works intermittently



## Merlin803

I have a staircase that goes upstairs that has a light on the ceiling and there is a switch at the bottom of the staircase and one at the top of the staircase that controls the light. 

Just lately, both of the switches will only turn the light on sometimes.

Is this most likely a problem with one or both of the switches? The fixture?

Thanks for any advise!


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## edhicks

Start with loose bulb, then fixture connections.


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## Merlin803

Checked the bulb and it is fine, I guess I will have to dig deeper. Would it be more likely to be an issue with the fixture or one or both of the switched?


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## Koot

As 'edhicks' suggested, check the lamp (light bulb) first. Not only could the lamp have become loose in its socket, but the filament could be broken and is intermittently making contact inside the lamp's glass envelope...

Switches only fail to two reasons; mechanical failure or electrical load contacts breakdown failure. Most switches have a 50,000 cycle On/Off life span, which it is doubtful that you have surpassed that number. Also, it's doubtful that your light fixture pulls very much amperage, or has a strong inductive load, that would cause the switch's load contacts to fail early. The problem could be one of the the switches, but it's usually something else...such as the lamp itself or a loose wire connection.

Since you have a 3-way circuit that uses two 3-way switches (one at the top of the stairwell & one at the bottom of the stairwell) you might be able to determine if the intermittent light problem happens when one of the two switches have their toggles in the Up or Down position.

Here is a simple wiring diagram of a 3-way switch circuit, where hopefully you can see how each switch (Sw# 1 & Sw# 2) must be oriented (in position A or position B) to feed voltage to the light fixture's lamp.










I'll bet you my jet-pack flying squirrel suit that the problem is not either of the two switches themselves.


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## Merlin803

Thanks! I switched the bulb and it did not resolve the issue so this weekend i'll probably take the fixture down and start there.


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## Koot

Merlin803 said:


> Thanks! I switched the bulb and it did not resolve the issue so this weekend i'll probably take the fixture down and start there.


Before doing anything with the light fixture, do the following...it might save you some time.

Remove the wall plates on the two 3-way wall switches. Doing this will give you a little better ability to wiggle and jar the switches, as well as the wiring in the switch boxes. With the light fixture On and the lamp lit - prod, poke and jar the switches and the wiring to see if you can get the lamp to flicker or go out. You may find that a wire is loose or even broken inside a wirenut, or a wire is loose on one of the switch's terminal screws, or a wire is not making good contact if the wires are connected by using push-in terminals.

Also, you may want to take a look inside the load center to make sure all the hot wires are solidly connected to the circuit breakers, and all the neutral wires are solidly connected to the neutral bar terminal.

Any loose wire, or broken and slightly connected (touching) wire, is what you're ultimately looking to find.


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## Merlin803

What I found was that the light works if both switches are the down position. They do not work when both are in the up position and when I had them both up and tried to switch the upstairs back down, there was a electrical cracking behind that switch.

I assume that indicates a likely problem with that upstairs switch?


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## Koot

Merlin803 said:


> What I found was that the light works if both switches are the down position. They do not work when both are in the up position and when I had them both up and tried to switch the upstairs back down, there was a electrical cracking behind that switch.
> 
> I assume that indicates a likely problem with that upstairs switch?


The electrical crackling (sparking) sound may, or may not, mean there's a problem with the switch or the wiring at this switch. It's somewhat common to hear a sparking sound when the switch's internal contact 'makes' or 'breaks' a circuit that is under load (pulling amperage). However, if you hear the electrical crackling/sparking sound without moving the switch's toggle...that means there is a loose wire somewhere.

Have you removed the switch cover and tried pushing/pulling (prodding/jabbing) the wiring to see if you can get the light to flicker or go out...or maybe to hear a crackling/sparking sound?

It sounds like you may have a loose or broken wire on that switch. Can you tell if the wiring is hooked on the terminal screws, or if they are connected to the switch using the push-in terminals? Push-in terminal connections on wiring devices are not the best, and oftentimes cause poor (loose) connections. Also, poke and move the wirenuts because it is commonplace for a wire to become broken or loose where the wires are twisted and connected within wirenuts.

It sounds like you are narrowing down the location where the problem is. Good work! :up:


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## Merlin803

I removed the top switch cover and it was pretty black and had what looked like soot on the switch and back of the cover so I put a new 3 way switch in to replace it. 

The good news is the light works consitantly and there are no sparks or funky sounds, lol.....but both switches still have to be in the bottom position for the light to work.

Now I am thinking I should replace the bottom switch too since it looks to be about as old as the one I replaced.


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## Koot

Merlin803 said:


> I removed the top switch cover and it was pretty black and had what looked like soot on the switch and back of the cover so I put a new 3 way switch in to replace it.
> 
> The good news is the light works consitantly and there are no sparks or funky sounds, lol.....but both switches still have to be in the bottom position for the light to work.
> 
> Now I am thinking I should replace the bottom switch too since it looks to be about as old as the one I replaced.


Well, as suspected, changing the switch did not solve your problem. I'd go ahead and change the other switch...and maybe you'll find the loose/broken wire you're looking for at the other switch, or in the other box. Don't forget to probe/prod/jab the wiring in the box to see if you can get the light to flicker or go out. This will tell you where the loose/broken wire, or poor wiring connection (at the switch or wirenut), is located. You have successfully narrowed the problem to a wiring connection in one of the two boxes/switches. It is not in the light fixture or in the ceiling box.


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## Drabdr

Merlin803 said:


> I removed the top switch cover and it was pretty black and had what looked like soot on the switch and back of the cover so I put a new 3 way switch in to replace it.
> 
> The good news is the light works consitantly and there are no sparks or funky sounds, lol.....but both switches still have to be in the bottom position for the light to work.
> 
> Now I am thinking I should replace the bottom switch too since it looks to be about as old as the one I replaced.


Are you sure you put the wires back on the same place as before?


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## Merlin803

Drabdr said:


> Are you sure you put the wires back on the same place as before?


Yep, positive. It is working exactly like it did before I replaced the switch. It is exactly as the diagram above.


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## Drabdr

Merlin803 said:


> Yep, positive. It is working exactly like it did before I replaced the switch. It is exactly as the diagram above.


Are you sure you put the wires on the right screw?

Sorry to be nagging.  it's just when someone changes out a three way and it works differently, most everytime a wire went on the wrong screw.

I would stress Koots advice about pulling out the other switch and wiggling the wires. Visually inspect the wire connection to see if everything looks good. Rarely is the light fixture the problem, except if the installer pulled the insulation out of the light and it gets too hot. Sometimes too , people put too big of a lightbulb in (too high of wattage).


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