Combine chili sauce, grape jelly and mustard in crockpot; stir well. Cover and cook on High while preparing meatballs. Add cooked meatballs to sauce in crockpot. Stir well to coat, cover and cook on Low for 6-10 hours or High for 4 hours. (Low is recommended.) To serve as appetizers, make small meatballs and serve on toothpicks. To serve as a main meal, make regular size meatballs and serve over flat noodles.