Work through these in order:
- Hopper seated correctly — most models have a safety interlock; the motor won't start if the hopper isn't locked in.
- Beans bridging — oily beans can bridge above the burrs. Tap the hopper or stir gently.
- Foreign object — a small stone can jam the burrs. Empty the hopper, remove the top burr, and check.
- Motor hums but nothing moves — switch off immediately and raise a warranty request.