[rohrmann]

The likely cause of the problem is that you just had the cylinders filled and now the furnace doesn't work. When you open the valves on the cylinders too fast, the excess flow valve in the pigtail nut closes off, but still allows enough gas to make the water heater and the burners on the stove to work, but not enough flow for the furnace to work. Turn off both valves on the cylinders, remove both the pigtails from the cylinders, then reattach the pigtails and SLOWLY open each valve. Once that is done, see if the furnace will light.