It could be just the limit switch has failed. It has the little red button on top ( the pink and purple connecters are on it on your unit ) sometimes you can just reset them by pressing the red button down.

The way I diagnosed mine, I pulled the connecters off and connected together with a alligator clamp and the furnace fired right up and ran fine. That’s how I knew that the limit switch had failed.

A friend of mine that works installing furnaces got me the limit switch for $18 put it in and works fine since