My furnace will not stay lit. The thermostat trips; the fire box fan removes all gasses; the glow plug gets hot; the natural gas is released and ignites; the glow plug starts to dim and the flames turn off. This series of events repeat two or three more times. Then the furnace stops the green LED changes to red; flashes seven times pauses and flashes seven more times. The Red LED sequence repeats for some unknown time. It times out and starts the whole process over again. What do you recomend?