Whisk 3 cups warm water with chicken soup base in slow cooker until soup base has dissolved; stir in cream of chicken soup until almost smooth.
Stir potatoes, ham, corn, yellow onion, and butter into the soup mixture.
Place flour and 1/2 cup water into a small container with a lid and shake well to combine into a smooth mixture; stir flour mixture into soup. Mix in parsley, dill, and celery seed. Season soup with salt and black pepper.
Cook chowder on High for 4 hours or Low for 8 hours, stirring once or twice during cooking.