I have a Trane XL80 furnace,the igniter is at one end and the flame sensor at the other. When the thermistat asks for heat,the fan kicks in the igniter glows then you here a click an you see the burners go on. My problem is sometimes it doesn't come back on, I watch to see if I can pin point problem but can't, the igniter glows an I hear the click noise from I guess the gas pump but the burners don't light.. I have to remove cover move gas inlet switch to off wait five min. then try again. Sometimes this works.when burners don't light should fan shut off because it stays on blowing cold air. I removed flame sensor an igniter an cleaned with emory cloth, but still have problem,sometimes it works . Please help me out.