depending on the model...many kettle stirrers have the ability to slide upward when they encounter a jam...at which point they no longer stir. it is a safety mechanism to prevent ruining your motor or damaging the stirrer. many of them also have a heavy nut that slides over the top to hold them in place. ensure the kettle does not have carbon buildup or other crud that is keeping the stirrer from turning freely. and ensure that the stirrer is functioning properly. if you need to clean your kettle an easy and safe way is with hydrogen peroxide and baking soda mixture. place in kettle and turn on heat and stirrer. place rags/towels in the bottom of your machine as it will bubble up. after a few minutes turn off the heat, unplug and scrub gently any remaining buildup with a non-scratch cloth. rinse and clean with warm water on a cloth. it will look like new without harming your finish...and easy food safe cleanup. also make sure your flapper doors are working freely to allow the popcorn to come out of the kettle. careful using a knife as you do not want to scratch your kettle.