In 12-inch skillet, heat oil over medium heat. Cook beef in oil until brown on all sides.
In 4- to 6-quart slow cooker, place potatoes, carrots and onions. Place beef on vegetables. In small bowl, mix horseradish, salt, pepper and 1 cup water; pour over beef.
Cover; cook on Low heat setting 8 to 10 hours.
Remove beef and vegetables from cooker; place on serving platter. Cover to keep warm.
Into 2-cup measuring cup, pour juices from cooker; skim excess fat from juices. Add enough water to juices to measure 2 cups; pour into 2-quart saucepan. In tightly covered container, shake 1/2 cup cold water and the flour; gradually stir into juices. Heat to boiling, stirring constantly. Boil and stir 1 minute. Serve gravy with beef and vegetables.