The KitchenAid immersion blender model 4KHB* is susceptible to a worn coupler. When this happens, the motor turns but the blade remains still. This may be caused by wear on the plastic coupler ribs that engage the 2 steel rotor teeth. To the best of my knowledge, no spare parts exist for this product. Good news is that repairing it is fairly easy using a 4 or 5mm thick washer, a saw and a pair of pliers…