Hello. The most common reason for your problem, which actually is that your burner is not firing up and staying on as it should, is that your electronic ignition device is not operating. In other words, your furnace is not igniting thus no heat. If you are mechanical you could open up the mechanical door on your furnace and check your ignitor. It could be dirty or it could be worn out. If you are not into mechanical things I recommend that you call the company that provides you with gas. They will send out a technician who will try to get your furnace going or at least pinpoint your problem so you can call in a repair person. Generally this is a free service. Start with that phone call. Good luck with it. Regards, Joe