I thought the thermostat was burned out too, but when I connected it to my downstairs unit, it worked just fine. Yes the stat requires 24 volts, I think. I'm not sure what you mean by "a common to your stat." I think there's a sensor that trips my power when there's a certain amount of water.
I'll try to put my R & W back into the correct slots and see if my thermostat starts back up since the furnace has been running for a while.