In crockpot, mix the potatoes, carrots, onion and celery. Toss the beef with the flour to coat evenly. Add to crockpot. Top with the tomatoes with their liquid mixed with the red wine, dry mustard, thyme, and pepper. Cove rand cook on high 1 to 1 1/2 hours. Reduce the heat setting to low and cook 7 to 8 hours longer, or until the beef is tender, stirring once or twice during cooking, if possible. Season with salt to taste.