Thanks for all of your help on this. I have decided to throw in the towel and call in a pro. When I tried to unscrew the switches, they did not move. Then I realized that there is a salty looking material that is slowly falling out from the seams in the exhaust piping as it leads away from the furnace. I am concerned that I have a major problem and that the switches are doing their jobs. It's a little scary that the system is only 6 years old. Thanks again.

Yep those 1/4 hex head screws can be a tuff one once in a while. These new furnaces are supposed to be professionally serviced every year but no one ever calls for service. LOL Your heat exchanger should be under warranty so that will save you big bucks for the part.

Had a HVAC tech out yesterday. He said that I have a design problem with my system. Said there were 2 "deadheads" in a row, coming out of the furnace, thus restricting air-flow. He noted that the system was designed to raise the temp 30-60 degrees and he measured it running at 58, which was close to the limit switch flipping.

The tech lowered the gas flow and switched my blower from high to medium, which was not right for winter time anyway. This required a rewiring at the circuit board. He was able to lower the temperature change to 54 degrees. The system has not shut down unexpectedly since. The tech made it sound like unless I had some new duct work installed the problem may continue. It should be noted that I was not all that impressed with the tech. But he did apparently alleviate the problem for now. Cost me about $132.

I believe it. Most furnaces are not installed properly and if you cannot see the entire install like from here using this board it would have been impossible for me to figure it out. It is a sad situation that the HVAC industry has got into over many years. I try to do my small part during my speciality classes at the university but since I keep the classes very small so each person gets hands on and personal treatment from me the number I touch every year is very small.

It seems you found a HVAC person who at least figured it out even if you were not impressed and the price you paid is cheap considering what would have been charged by others. Eventually you will have to fix the duct problem and that you might do when you eventually replace your unit since it will be cheaper to do at that time.

HINT: You can always pop a relief hole in the duct right above the furnace to help prevent overheating. This will just dump hot air in the furnace location but it is better than having it shut off from over heating.

Always remember