[Mikeron]

The downstairs switch will not work unless the upstairs switch is flicked up.

What could be the problem?

 

[oh'mike]

You have a couple of wires on the wrong terminals----

An electricial will be along soon---do you have a two wire tester?

 

[Oso954]

One of the traveler wires has been switched with a common at one of the switch locations, or one of the travelers has been broken or shorted.

When did the problem show up and what if any work had been done on or near it about the same time.

 

[joed]

Did this ever work properly? If it did and no work has been done, then you have a defective switch.