How do you fix a open high limit device in an american standard freedom 80 furnace? Is it expensive?

troubleshooting 4 flashs indicating open high limit device. Can this be repaired by myself or do I need a professional to do this? Will this cost a lot of money to repair? American Standard Freedom 80 furnace.|||Your furnace has more than one limit switches. These are safety controls designed to open up the ignition circuit in the event of overheating. Something is causing the furnace to overheat. For the DYI, I would recommend you check the filter and the vent to see if either is restricted. You will need to power down the furnace to reset the fault condition. Outside of that, call a licensed technician. The cost to repair this should be somewhat modest.|||I would love to give a simple answer, but, it depends on the type of limit switch, and what caused it to go open. It may not be bad. It may have opened like it is designed to do to prevent overheating. Reset the alarm indicator. You will have to figure out how to remove power from it for a few minutes. It probably has a battery back up, so this has to be removed as well. If, after all this you turn the furnace back on, and it flashes again, you will have to call the man.