I am still trying to get this Trane XR80, Propane, horizontal updraft furnace to work. Quick recap. I found the furnace blower only running, no heat. Diagnostic of Check Ignitor, so I replaced the ignitor and flame sensor and shortened and put a new connector on the wire to the flame sensor as the last two inches of wire to the sensor were badly charred. Now I got the "open high limit device", 4 flash diagnostic. I've tried the fix of hitting the attaching screw three or four times but no luck. I did see some evidence of soot on the flame sensor wire when I looked into things today, but not charred, just slightly sooted. I see that there are other devices, they look like "buttons", that appear to be on the same circuit as the High Temp Switch. Are these "High Limit Devices" too? The water is still flowing in this apartment but with the temps getting so low, I am concerned about freezing.It is a 20 mile drive to the Trane parts supplier so I want to minimize trips. Thanks for any help and or advice,
Tony

PS I should add although the furnace did try to start last week, that the furnace does not even try to fire now, there is no smell of propane even though there is 25% fuel in the tank (I know this is low but figure no virtue in getting more fuel while the furnace doesn't work ). I feel that this is because the high limit device locks everything out. Am I correct in this? When diagnosing the igniter, the furnace would try to fire but shut down a few seconds after firing.

Not ansering, adding some info. I saw on another forum that a continuously running blower can be an indication of a faulty circuit board. I have already priced the board and will but one if that's what is needed but don't want to buy any parts needlessly or make two trips to the Trane supplier. Any help please!

I'm closing this thread. I found out what this problem was, and found another. This problem was with what I believe is called a "rollout" switch. It's located just behind the burners, it's about the size of a dime with a small, light brown plastic piece that has a part that sticks out of the body of the switch. Pushing in on this raised portion reset the switch and the furnace then fired up and appeared to work correctly. After a while I found that there was cold air coming from the registers and the same 4 flashes from the diagnstic light. I also found that there was even more soot, even burned area on the wire going to the flame sensor. Afetr holding down the safety switch and firng up the furnace, I can see that the lowest of the three burners was burning "lean", yellow and featery rather than the solid blue of the center and upper burners. I believe that the lower tube of the heat exchanger is rusted and/or perforated. I am going to look for an exploded parts view and whether the tube itself can be replaced.