The 'normal' way for a light with multiple switches controlling it is that ANY switch will toggle the light on/off. It doesn't matter if the switches are up or down. If the light is off and you flip any switch (up OR down) then the light goes on. Similarly, if the light is on, then any switch will turn it off.

It's also possible that someone wanted to have a master switch that requires it to be on in order to operate the light, but the convention (at least in North America) would be down==off, up==on. So the odds are that your behaviour isn't the original intended behaviour.

But there's no way to give you a definite answer without knowing more information.

Possibilities:

(1) It was never wired properly

(2) A switch is malfunctioning

(3) Somebody mucked with the wiring at some point and screwed it up. Maybe they tried to replace a switch and put it back wrong.

The easiest problem to fix is if it's (2). Then you can just replace the switches and see if it works properly. If you do this, replace them with EXACTLY the same type of switches and make sure that you attach the wires in EXACTLY the same manner. You don't want to be responsible for creating situation (3). I'd suggest taking pictures before you detach anything.

"When sw 3 is in the up position, the other two sw cannot turn the light on"

Pull this switch out but don't take it off the wires. Take a picture and post it here. Make sure to get a picture of where the wires come into the box so that we can see which wires are in which cable.

There is something not wired up properly in the 4 way circuit, most likely problem is with the way a switch was wired (maybe sw 3), assuming multi-way switches were used.

The following is an online link describing 4 way switch operation.

http://www.act-solutions.com/PCC/kingery07.htm

Thanks. I couldn't get a decent picture. Either it was too dark in there or the flash washed it out. This is the way the sw is wired:

........... Left.. Right

Top White 1 Red2

Bot white 2 Red 1

Most 4-ways I've seen want the one pair of travellers on the left and the other on the right. Try interchanging the two bottom wires.

It sounds like it is wired like the top picture.

It should be wired like the bottom diagram. You need to pay attention to the color of the screws, and from which cable the wires originate, and not the color of the wires. Top set of screws are a different color than bottom set.

I think I have seen an occasional switch where the left screws are one color, and right another, but rarely.

It would be advisable to use a multimeter to check which is the hot wire.

If you're uncomfortable/ unfamiliar with making the fix, have a local electrician fix the issue.