Limit switch doesn't function on oil furnace
The high limit being taken off the wall of the fire box it will never over heat.
Try removing 1 of the leads to the switch if the furnace keeps running it is not the limit switch.
Most of these limits have a manual reset button you need to press if they do overheat.
If the furnace keeps going with the limit wire removed you need to have the controls fully checked out as this is a safety hazard.