The gas valve should kick off as the ice is coming off when the curtain switch opens due to the ice pushing the door. If your ice is hanging on the plate after it has pushed the curtain open enough to open the switch, then your plate is dirty(common) or you have plate/tubing seperation(not common on that model). You can only use nickel safe cleaner on that machine or the nickel coating will come off. What does the plate look like? Harvest should take anywhere from 1-2 minutes.