355 MAV Furnace
doesn't a tripped hi limit close to energize the fan? Then open to stop the fan once the heat exchanger has cooled off, therefore wouldn't that be a hi limit that isn't opening/is stuck closed? AND if so does that also prevent start up therefore, there is another set of contacts that open and cut off the limit/start up circuit? Therefore it is a hi limit tat won't close. I think I just answered my own question but, hopefully this helps the OP,
First part of fix is to replace the Hi Limit.