I have a concord 80 plus furnace. Its less then 2 years old. It will not blow hot air, and the motor just runs and will not shut off no matter what the therm is set at. The LED flashes 4 times which says "open limit switch or limit switch circuit". I pulled the limit switch out (at least I think it's the limit switch. About 2 1/2 x 2 inches. Brown board with 2 wires going to it). I was searching the web and can't get any clear answers. Should I just replace this switch, or should I check something else?

Thanks in advance for any responses.

If you can electrically test the device, do that first also check inline (follow the wires) to other switches in the circuit, possibly a draft safeguard , mounted by the flue and ventor motor.

The fault code may be associated with other safeties.

There may be pictures or a description of the limit switch in the sticky at the top of the H&AC forum.

Your description of the limit being a brown board with two wires going to it sounds like you have the right thing. Did you find this up on the wall of the furnace below the vent pipes?
You can check this limit with a jumper wire, with the thermostat on and the blower blowing touch the metal spade clips that the two wires, use the jumper wire, if the blower stops and the vent motor kicks in (That is if you have one). If this happens that means your limit is bad, one more thing. On one of the wires connected to the limit do you have a small thing about an inch long, that looks like a small firecracker. If you do then use the jumper wire and touch one each end of the fuse, make sure you are touching metal, it the motor starts this is your problem. DO NOT UNDER ANY CONDITIONS LEAVE THE JUMPER WIRE CONNECTED TO THE LIMIT OR THE FUSE.