[cgarr]

What Ruf said, is the gas lighting? if so then the flame sensor is not working and it will shut down, usually just some sand paper across it will fix it, its just a steel rod on the opposite side of the ignitor. That way all the burners have to light before the system accepts all is well.

If the ignitor is bad and not lighting up you can manually light the furnace when the gas kicks on and at least warm the house for a bit.

After it tries three times and fails you will need to shut the power off to the furnace and back on to reset the controller. Then it will cycle again.