For some reason, a light switch in my basement (under construction home theater) doesn't always work. There are two switches connected to this circut that can be contolled from the top or bottom of my stairs. Lutron switches. sometimes they work, sometimes they dont. Any thoughts? contractor (cousin's company) will be bank in a few days to look at it.

bad switch

Or a miswired three way. I've done that by accident before. Turns on at one location, nothing at another.

When it "doesn't work" have you tried the other switch?

Sure sign of crosswired switch. Just reverse the wires on the added switch and it should correct the problem.This is as long as you used a 3-way switch as your added switch and not just a single pole switch.

Agreed with the above. It sounds like a 3-way switch which is easily miswired. Even worse, are 4-way switches!