My xr80 furnace, when the fan is in the auto position, will not stay lit. it flames up for ten to fifty seconds but will not stay lit. when I turn the fan to the on position, it flames up and stays lit. I cleaned the furnace and filter. What could it be? What else can I do?

my xr80 furnace, when the fan is in the auto position, will not stay lit. It flames up for ten to fifty seconds but will not stay lit. When i turn the fan to the on position, it flames up and stays lit. I cleaned the furnace and filter. What could it be? What else can i do?

This must really be a tough question! One month , 85 looks and no response. Wow!

My is doing the same thing