My furnace won't stop blowing air I don't know what's going on it's never done this before, it just starting doing it one night. The thermostat says it's on sleep and I turned the furnace off at the thermostat but it's still blowing. It's only blowing cool air. The model is a concord 90 plus and I'm guessing it's only a few years old what should I do to fix it?

You should have a light blinking on the control board that will give the fault code. If the blower is on all the time and not heating you have or have had a open limit, the blower will run all the time to let you know you have a problem.