Furnace stopped working

It could be clogged with rust. My brand new one did the same thing after only 3 months. The burner tubes are thin metal and after using them a time of two, the paint burns off of them created a dust. Then the tube rusts on the inside creating more dust. All I had to do was take it out and take it apart, not hard to do, and blow it out with an air hose. You'd be amazed at how much "dust" and rust came out of it and it brand new. Works well now.

could be a number of reasons, limit switch, sail switch low battery or bad battery, gas valve.

Put this under the tech section you will get better response. Also, make, model etc.