Blenders that see a lot of use are at risk for a broken clutch. Over time, the teeth on a commercial blender clutch will wear down until the clutch no longer engages properly with the blade assembly. If you hear a grinding sound, or if your blender's blades no longer spin at all, it's time to replace that clutch. Don't bother with a service technician! You'll find this DIY task easy, and cost-effective.