Diagnosis
The most common cause of a leaking Nutribullet cup is an improper seal between the cup and the extractor blade assembly. This usually happens when the blade unit isn't screwed on tightly enough or when the rubber gasket (a small black ring on the blade base) is missing, damaged, dirty, or out of its groove.
How to Fix It
First, ensure the blender is unplugged. Disassemble the cup and inspect the black rubber gasket on the blade base. Clean it thoroughly, making sure it's seated correctly in its channel. Reassemble by placing the blade unit onto the cup and twisting it clockwise until it's hand-tight—don't use tools. To create a proper seal on the motor base, place the assembled cup upside down onto the base, press down firmly, and twist clockwise until it locks securely. When testing, run the blender for a short burst with the blade pointing away from you for safety.
If That Didn't Work
If leaks persist, the gasket may be worn and need replacement (available from Nutribullet). Also, check the cup itself for hairline cracks, especially around the rim. For older models, the plastic threading on the cup or blade unit can become stripped, preventing a tight seal; this requires replacing the damaged part. Ensure you're using the correct blade assembly for your cup size, as mixing parts can cause leaks.
Heads Up
Never operate the blender if liquid is visibly leaking, as this poses an electrical hazard. Always let the blender run for its full cycle and allow pressure to equalize (about a minute) before attempting to open the cup, especially after blending warm ingredients.