What is your fuel type: gas or oil. If you have gas, your ignitor would be your problem. Look into the glass in front of the burners. My igniter is on the left side. If the igniter does not glow cherry red, the whole igniter, the temperature sensor will not open the gas valve. Look at the control module flashing light. This tell you what the cause of the failure, quite simple. Go the the York web page and download the manual for your furnas. A new ignitor locally $60, web best $30. Keep a new one just in case. I was impatient at midnight, so I used my propane torch instead of the ignighter to light the furnas. Kids get cranky at 50 degrees in there PJs.