2 way light switch problem after building work

[katheh]

I recently had some building work done on my house and now a 2 way switch right next to where the building work was is not working. I noticed the problem an hour after the electrician left from the final fit but he claims he didn't touch it and it can't be him (there was significant rewiring but this light should not have been touched).

Now the light only works on one switch at a time so the switch positions result in:

Up Up - Light off
Up Down - Light On
Down Up - Light On
Down Down - Light On

Electrician has been back and checked switch wiring which he says is fine. Says there must be a junction box somewhere inaccessible under upstairs floorboards in an area not covered by the works and it can't have been him.

Is there anyway this could happen by accident (e.g. builder drilling through a cable)??? I can only think that it must have been inadvertently rewired somehow.

Thanks in advance.

 

[EFLImpudence]

A picture of both switches - so we can see where each wire goes - may show something.

 

[katheh]

 

[EFLImpudence]

Sorry, they seem to be wired correctly.

As the cable can't just run between the two switches, there must be a JB somewhere or connections at light positions.



It could be a faulty switch. Does it feel like it works properly?

Do you have a multimeter?

 

[katheh]

I think both switches work because they both can turn the light on and off as long as the other switch is in the right position. The electrician said the same about the junction box. Light fitting just has a single live, neutral, earth coming into it.

I don't have a multimeter.

Is it feasible that the junction box would be under carpet/floorboards upstairs? I thought they had to be accessible.

 

[katheh]

What is really puzzling me is that I would have thought something getting broken, like a wire being cut, would lead to the light being more likely to be off than on but 3 out of the 4 switch combinations leave the light on.

 

[EFLImpudence]

I think both switches work because they both can turn the light on and off as long as the other switch is in the right position.

I am a bit confused now.
According to the original post, downstairs had no effect -
Up Up - Light off
Up Down - Light On
Down Up - Light On
Down Down - Light On

Is it feasible that the junction box would be under carpet/floorboards upstairs?

It could be anywhere.

I thought they had to be accessible.

They do now for this very reason.

 

[katheh]

I think both switches work because they both can turn the light on and off as long as the other switch is in the right position.

I am a bit confused now.
According to the original post, downstairs had no effect -
Up Up - Light off
Up Down - Light On
Down Up - Light On
Down Down - Light On

So if both switches are in the up position (that might not be the correct term) the light is off. Moving either switch to the down position will switch the light on. This is what makes me think both switches work as they both do something, just not the right thing collectively.

The problem is when they are both in the down position the light stays on rather than going off.

 

[EFLImpudence]

So if both switches are in the up position (that might not be the correct term) the light is off.

Ok. That's right.

Moving either switch to the down position will switch the light on.

That's right too.

This is what makes me think both switches work as they both do something, just not the right thing collectively.

That would seem to be true.

The problem is when they are both in the down position the light stays on rather than going off.

Right, I'll have to have a think. That does seem strange (impossible).

 

[Mikefromlondon]

From the logic described it is apparent that the incoming live feed has been incorrectly connected to either L1 or L2 on one of the switches, and it would be the switch that first receives the incoming live.

Incoming live should be wired to Com terminal.

Problem can be quickly fixed by swapping the wires on the switch that receives the incoming live by swapping Either L1 with Com OR L2 with Com.

As there are no Neutrals involved in a switch, swapping wires cannot result in any hazard apart from it may not work correctly.

 

[EFLImpudence]

Ok. I think -

at one of the switches the Com and one of the other wires are the wrong way round.

It's not possible to tell which from here.

 

[EFLImpudence]

From the logic described it is apparent that the incoming live feed has been incorrectly connected to either L1 or L2 on one of the switches, and it would be the switch that first receives the incoming live.

It would be the same with the outgoing live so could be either switch.

 

[katheh]

Ok. Thanks both. I'll try this in the morning and see what happens.

 

[Mikefromlondon]

From the logic described it is apparent that the incoming live feed has been incorrectly connected to either L1 or L2 on one of the switches, and it would be the switch that first receives the incoming live.

It would be the same with the outgoing live so could be either switch.

Possibly, Efl, but I drew the 2 way switch schematic on a piece of paper and wired the live to one of the L1 terminals and from it you could clearly see you would get exactly the logic pattern that has been described by OP. (Sorry didn't intend to prove anyone wrong or anything just trying my bit to help)

Often if one jots down a problem on paper, it can become more apparent, other times experience would kick in and say yup i know what the problem is, but one can only get experience if thousands of 2 way circuits were wired incorrectly and one had to fix them on a daily bases.So theory cuts in.

 

[ban-all-sheds]

So if that's the cause, and we assume (reasonably??) that it wasn't like it before, who changed it?

I can only think that it must have been inadvertently rewired somehow.

Nobody "inadvertently" unscrews switches and swaps wires over.

Did the building work involve any painting of the wall(s) the switch(es) are on?