A blender that suddenly roars without moving anything is almost never broken. It has an air pocket under the blades, and the mixture above is bridging across the top like a badly packed suitcase. The fix costs nothing and takes five seconds, but it depends on the order you put things in the cup.
Liquid first, always
Whatever the cup shape, liquid goes in before solids. It surrounds the blade assembly, transmits motion outwards and lets the vortex form. Load frozen fruit onto a dry blade and the machine has nothing to grip, so the motor spins hard against a solid plug of ice.
Then soft, then leafy, then frozen
After the liquid, add yoghurt, banana or soaked oats, then leaves, then the frozen items last. Spinach and kale sit in the middle where the vortex actually shreds them. Ice on top uses its own weight to drop into the blades as the mixture thins, which is exactly what you want.
Inverted cups change the rules
Personal blenders where the cup screws onto the base upside down reverse everything: fill in the order you want it to meet the blade once flipped, which means frozen items go in first and liquid last. It feels wrong the first three times. The cup and blade layouts in the KOIOS personal range are shown at https://koios.us.com/, and looking at the geometry makes the logic obvious.
Do not overfill
Two thirds is the practical ceiling for cold ingredients, and half for anything warm. A full cup has nowhere to circulate, so the top layer never travels. Overfilling also strains the gasket, which is how people end up with smoothie under the base.
When it still stalls
- Stop the motor, do not hold the button hoping it clears.
- Unplug or remove the cup before poking anything inside.
- Add a splash more liquid rather than more force.
- Shake the sealed cup once to drop the bridge onto the blades.
- Restart in short pulses instead of one continuous run.
Pulsing is a technique, not a gimmick
Three or four short bursts break up a frozen mass far more effectively than ten seconds of continuous running, and they let the mixture fall back onto the blades between bursts. Continuous running should come after the mixture is already moving. That habit alone extends motor life noticeably.
Respect the run time
Domestic blender motors are rated for short duty cycles, commonly around a minute of continuous work, then a rest. Ignoring that is the most common way a machine dies in its first year, and the smell of hot varnish is the warning you get. If the housing is too warm to hold comfortably, put it down and make toast instead.