Gas and Oil Home Heating Furnaces - Goodman furnace will not run

My Goodman furnace is propane forced air. It's old,14 years. I replaced the ignitor and it works fine; found the top roll out limit switch open. I closed it and it worked fine, once. Replaced the limit switch and it worked fine for one day. The heat exchanger has no cracks in it and I cleaned the flame sensor. What does the limit switch sense and control? I know that it's a safety feature to keep the box around the burners from over heating but since the switch is new, what else do I need to look at? The blower works fine, I just can't seem to keep the limit switch closed.

If the spill switch continues to trip it could be an indication of a defective heat exchanger. More than likely the crimp rings that hold the heat exchanger cells together have popped. This allows burner spillage when the blower starts and causes the switch to trip. You should have a competent service company look at your furnace as a defective heat exchanger could lead to carbon monoxide issues.

This is a flame rollout switch inside the burner compartment right above the burners? Do you see any flames backing out of the heat exchanger when the furnace turns on?

Goodman furnaces are so crappy. Perhaps you should splurge and hire a plumber!