Is the Igniter working? Take off the top panel so you can see the burner. Turn up the thermostat to call for heat. Do you see an orange glow and hear gas coming out before it shuts down? If no orange glow then your igniter is probibly shot. If you see an orange glow and hear gas comming out, but the furnace still doesn’t light, the roll out switch is probibly shot. You might need a repairman to fix it.