Nuova Simonelli grinders, mainly the MDX and Mythos series, fail in a handful of predictable ways. Most problems trace back to burr wear, motor load, or calibration drift. Here’s what’s actually going on, and what a tech is looking for when one of these machines comes in.
Inconsistent Grind and Channeling Shots
Most common complaint. Shots channel or run fast and sour even though the grind looks normal. Usually it’s the burrs.
The Mythos One uses 75mm flat burrs; the Mythos Two runs 85mm titanium. Flat burrs are less forgiving than conicals once they start to dull. On a busy bar, you’ll notice performance drop before the burrs are technically worn out, especially with dark oily roasts. Oily coffee accelerates glazing on the burr faces, which causes clumping and uneven particle distribution.
The MDX uses 64mm flat burrs. Same principle, but smaller burrs can show wear faster under heavy volume.
What a tech checks: Burr condition visually and by touch (rounded edges, glazed faces), grind retention in the chute, and burr alignment. A misaligned burr set produces bimodal grinds even with fresh burrs.
Burr replacement on these grinders isn’t a straightforward swap. Reassembly has to land the burrs in correct alignment or shot quality gets worse, not better. Worth handing off to someone who does it regularly.
Motor Not Starting or Stalling Mid-Grind
If the motor hesitates at startup or stalls partway through a dose, start with the obvious: is the grind setting very fine? Running extremely fine with clumping coffee can overload the motor. Coarsen it slightly and test. That’s the one check worth doing yourself.
If that’s not it, you’re looking at a failing start capacitor, worn motor brushes (on brushed-motor models), or a packed grind chute creating back-pressure. The Mythos Two uses a brushless motor, which eliminates brush wear, but the electronics driving it can still fail.
What a tech checks: Capacitor condition, brush length and contact on applicable models, motor amperage at startup, and whether the exit path is clear.
Motor and electrical diagnosis involves mains voltage. Don’t open the machine for this one.
Gravimetric Scale Issues (Mythos Two)
The Mythos Two doses by weight using a load cell in the portafilter mount area. When dosing goes erratic, fine grounds contaminating the load cell area is the first thing to check. These sensors are sensitive.
Also confirm calibration if someone recently swapped portafilters or dropped in a heavier aftermarket basket. A changed tare throws every dose off.
Cleaning the scale area and recalibrating per the manual is a reasonable first step. If it’s still inconsistent after that, the load cell or display board is likely failing, and that’s a parts job for a tech.
Dead Machine, No Display
Total power failure usually means the main fuse or the power board. First confirm power is actually reaching the machine. On the MDX, there’s a fuse in the base that’s accessible without tools on most versions. If the fuse is intact and the machine is still dead, the power supply board is next.
On the Mythos, the display and control boards are separate. A dead display with the grinder otherwise running points to the display board or the ribbon cable connection.
Anything past the fuse involves mains voltage. Call a tech.
Grind Adjustment Drifting
If shots creep faster during a shift without anyone touching the grinder, the adjustment mechanism is worn. This is a known wear item on the Mythos collar system and the MDX stepped mechanism.
Fixing it means disassembling the upper burr housing. If reassembly doesn’t get the burrs back in correct alignment, you’ve turned a calibration problem into a burr alignment problem. This is a tech job, not a barista job.
When to Call Us
Grinder faults compound. A wrong burr alignment or incorrect capacitor spec can turn a minor problem into a more expensive repair. If the machine is holding up your bar, don’t experiment.
Diagnostics can take up to a week; most repairs run 3–4 weeks. That is exactly why we recommend preventive maintenance: a maintained machine does not sit in a repair queue for a month.
For more on how we cover the brand, see our Nuova Simonelli grinder repair page, or our grinder repair service page if you’re running a different make.