How to clean concord 80 plus flame sensor

Use a fine sandpaper to polish it clean. Deposits build up on it and prevent it from working. Clean where it attaches to furnace, too. Make sure the tip is in flame so that it will sense when you put it back on. Rust and corrosion on burner will keep it from grounding properly and sensor will not work. You should be able to remove entire burner and clean it all out well and vacuum out heat exchanger, too. They are very easy to work on.