I have central heat and air and a gas furnace in my attic. Yesterday I noticed cool air was blowing out of my vents. I went up in the attic and noticed the furnace was on, just no heat. The warning label on the side said it doesn't have a pilot light but uses an electric ignition and had a procedure to do it. I just shut my thermostat to off and have not messed with it, any suggestions before I call a heat and air guy to come look?