Lightly grease the slow cooker. Add the broken dry vermicelli, chicken broth, condensed cream of chicken soup, and sour cream.

Stir until the soup and sour cream blend into the broth and all noodles are submerged.

Cover and cook on low for 1 1/2 to 2 hours, stirring once halfway through if possible. Check from 1 1/2 hours; the noodles should be tender and the sauce thick.

Stir again, rest uncovered for 5 minutes, and serve warm.