Place cubed beef and flour in a resealable plastic bag. Seal and shake to evenly coat beef with flour. Heat the oil in a frypan over medium heat and brown beef on all sides. Transfer to a slow cooker.
Melt the butter in the frypan over medium heat and cook onion until tender. Transfer to the slow cooker with the beef. Pour wine into the frypan to deglaze then pour wine into slow cooker.
Dissolve the beef stock cube in 1 cup hot water and pour into slow cooker. Place potato and carrots in slow cooker and season with rosemary, thyme, garlic powder and pepper. Mix in remaining water and Worcestershire sauce. Add more water if needed to cover all ingredients.
Cover slow cooker and cook stew 7 to 8 hours on Low.