I have a Frigidaire\Nordyne G6RA 096C-16 gas furnace. The electronic ignitor lights the gas. However, when the blower comes on, the gas shuts off. This happens repeatedly. I turned off the furnace, waited a few seconds, and turned it back on. It worked fine for the first thermostat cycle (until it got to temperature). When is kicked on again, the same problem recurred. Any suggestions?