Grindmaster Grind’n Brew Error Code Er3: Thermistor Error
Er3 is a thermistor error with the same description as Er2: the thermistor is open, shorted, or the water is boiling. It applies to the 2016 revision of the manual. Clear it by holding the UP key for 5 seconds, resetting power, or entering field test mode.
High: water fill and heat shut off and brewing is disabled until the thermistor problem is fixed.
- Code
- Er3
- Maker
- Grindmaster
- Equipment
- Coffee brewers
- Applies to
- Grind'n Brew GNB-10H/11H/20H/21H
What does Grindmaster error code Er3 mean?
Er3 reports the same thermistor condition as Er2 in this revision of the manual. The control reads the thermistor to know the water temperature, and if the thermistor is open, shorted, or the water is boiling, it shows Er3. With any of the water system errors, water fill and heat shut off and brewing is disabled, while grinding is still allowed. The display shows the error when the unit is idle and the Basket Out light flashes. The troubleshooting guide lists reprogramming the thermistor or temperature settings and replacing the thermistor. The code meanings differ between manual revisions, so this page follows the 2016 revision, BW-354-03. An older 1997 revision of the manual calls Er3 the heater error and has no Er4, so a brewer with that older manual should not be read the same way. To clear the error, hold the UP key for 5 seconds, reset power to the unit, or enter field test mode. A technician reads the revision of the unit before choosing the diagnosis.
Affected models and control systems
Grindmaster Grind'n Brew GNB-10H, GNB-11H, GNB-20H and GNB-21H. This page follows the 2016 manual revision (BW-354-03); an older 1997 revision gives Er3 a different meaning.
Code numbers and their meaning can change between control generations. We match the full model and control before acting on a code.
What you may notice
- Er3 on the display when the unit is idle
- Basket Out light flashing
- Brewing disabled
- Grinding still works
Possible causes
Listed in Grindmaster's documentation
- Problem with thermistor
Other likely causes — what usually sits behind error code Er3 on this control. A technician confirms which one it is before any part is replaced.
- Thermistor wire pinched or broken near the tank
- Connector corroded by steam
- Older brewer whose Er3 means heater, not thermistor
Safe checks before calling for service
- Hold the UP key for 5 seconds, or switch the power off and on.
- Let the unit cool if the tank is very hot.
- Try one brew.
- If Er3 returns, note the model and any label showing the manual revision, then call us.
How a technician diagnoses error code Er3
- Read the display and confirm Er3.
- Confirm the manual revision for the unit.
- Compare water temperature with a reference thermometer.
- Check the thermistor wiring and connector.
- Replace the thermistor if it fails.
- Interpreting the code depends on the control revision.
- Thermistor tests need a meter and temperature references.
- The tank area is hot and wiring is at line voltage.
How error code Er3 differs from similar codes
In the 2016 revision Er3 is a thermistor error; in the 1997 revision it was the heater error.
Technical reference
- Maker documentation
- Grindmaster owner support
- Edition
- Form # BW-354-03, 0516 (copyright 2016)
- Models / control
- Grind'n Brew GNB-10H/11H/20H/21H
- Section
- Programming section 'Water System Errors' (printed p.10) and Troubleshooting Guide (printed p.14)
- Checked
- October 2026
We use the maker's document to read the code and do not reproduce it. Always confirm the complete model and control before applying these steps.
Related Grindmaster coffee brewer error codes
Is Er3 a heater error?
In the 2016 revision it is a thermistor error. In the 1997 revision it was the heater error.
Is it the same as Er2?
In this revision the description is the same.
How do I clear it?
Hold the UP key for 5 seconds, reset power, or enter field test mode.
Need help with Grindmaster error code Er3?
A technician confirms the cause on site and gives you the price in writing before any work starts.