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Troubleshooting: False Chirp and Zero Point Shift on the Z2

Updated

Sound familiar?

Your shots gush even at very fine settings. You keep having to grind finer. The dial feels stiff moving from a pour over setting back toward espresso. You hear a chirp well above where zero should be, or your zero point seems to have moved.

What is happening

This is called false chirp, and it is a normal occurrence in high-precision flat burr grinders. Tiny coffee particles get packed into the flat finishing areas of the burrs. Coffee rubbing on metal sounds a lot like the true burr chirp you use to set zero. If you zeroed on that sound, your grinder is actually set coarser than the dial shows, which is why shots run fast.

Precise alignment makes this more likely, not less, because there is no wider gap on one side for grounds to escape. Some burrs are more prone to it. SSP Brew burrs, for example, tend to trap grounds in their middle row of teeth until they season.

Video: https://www.youtube.com/watch?v=75M2g-MhhoY

How to clear it

  1. Turn the grinder ON. Adjust only while it is running.
  2. Use Purge Mode (hold the switch down) while turning the dial 200 to 300µm coarser, then slowly back finer. The higher speed helps push out trapped grounds.
  3. Keep slowly turning finer. You will feel some resistance, which is normal with the grinder running. Stop as soon as you hear true chirp, a sharp metal-on-metal sound.
  4. Turn the grinder OFF and rezero (see Setting the Zero Point on Your Z2).

If the dial feels very heavy or will not move, do not force it. Open the grinder and clean the burrs and chamber instead (see Opening, Cleaning, and Closing Your Z2).

Keep it from coming back

Grind your finest brew first and move coarser through the day rather than sweeping from coarse to fine. Make all adjustments with the grinder running. Clean the burrs regularly.

Zero point shift

It is normal for the zero point to move slightly after you remove the front assembly, swap burrs, or while new burrs season. A 20 to 50µm change looks big on the dial, but a human hair is about 100µm thick. The dial shows the burr gap, not the particle size.

If the zero keeps shifting after you have ground about 5kg of coffee:

  1. Rule out false chirp using the steps above.
  2. Turn the grinder OFF and unplug it.
  3. Open the grinder and remove the burrs.
  4. Clean and reseat the burrs, making sure nothing is trapped underneath, and reassemble with the dial at about 100µm.
  5. Reset the zero point.

If these steps do not work, please contact support at info@zerno.co with a short video.