Can you tell me if the main blower that blows air out of the registers is running?
The code is for an open high limit.
Common causes are dirty filter, bad blower motor, plugged ac coil (if equipped)
Short story is the furnace is running too hot and is needing to shut down on safety and cool off...then it tries again.
If filter is clean and no registers are blocked I would recommend checking the blower for proper air flow.
This depends on the installation. It almost always requires the removal of the coil or sheet metal encasing it.
If the unit has always had good filters it is unlikely...but if the unit had a history of dirty filters then the ac coil is suspect.
You are most likely correct. Tighten any connections...use a pair of pliers to gently crimp slide on terminals.
You may also have a bad spot in the board.
Wait to see if it resets. Once cooled it should start again. In the event the limit becomes stuck you can try tapping it. It is located on front wall behind gas valve and has 2 wires attached. It mounts directly to the front wall.
You are very welcome.
The good news is that your furnace is very sensitive to safety related situations. It will let you know if there is a problem
I wish you luck....