We have a Janitrol furnace and for some reason we can't get it to light. We push the knob down, and when we went to light the pilot it won't light.

Thermocouple?

If it will not light at all, means you have a blocked piolit tube or orfice, or no gas comeing to the piolit, or air in the line. If it lights, but will not stay lite then the thermocupling is bad.