Grindmaster Grind’n Brew Error Code Er2: Thermistor Error
Er2 is a thermistor error: the thermistor is open, shorted, or the water is boiling. The manual groups Er2 and Er3 together. Clear it by holding the UP key for 5 seconds, resetting power, or entering field test mode, and have the thermistor replaced if it returns.
High: water fill and heat shut off and brewing is disabled until the thermistor problem is fixed.
- Code
- Er2
- Maker
- Grindmaster
- Equipment
- Coffee brewers
- Applies to
- Grind'n Brew GNB-10H/11H/20H/21H
What does Grindmaster error code Er2 mean?
The thermistor reads the water temperature, and the control depends on it to heat and to brew. If the thermistor is open, shorted or reads a boiling temperature, the control shows Er2. The manual groups Er2 and Er3 as a single thermistor error, so either number points to the same circuit. 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's remedies are to reprogram the thermistor or temperature settings and to replace the thermistor. To clear the error, hold the UP key for 5 seconds, reset power to the unit, or enter field test mode. A cleared error that returns means the thermistor circuit is still wrong. Because boiling water is one trigger, a unit that really overheated can show the same code as a broken wire. A technician checks the reading against a reference thermometer before changing the part.
Affected models and control systems
Grindmaster Grind'n Brew GNB-10H, GNB-11H, GNB-20H and GNB-21H. The manual lists Er2 and Er3 together as one thermistor error.
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
- Er2 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 Er2 on this control. A technician confirms which one it is before any part is replaced.
- Thermistor connector corroded or loose
- Thermistor wire damaged near the tank
- Temperature settings changed in programming
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 seems very hot.
- Try one brew.
- If Er2 or Er3 returns, note which one and call us.
How a technician diagnoses error code Er2
- Read the display and confirm Er2 or Er3.
- Compare the water temperature with a reference thermometer.
- Check the thermistor wiring and connector.
- Check the temperature settings in programming.
- Replace the thermistor.
- Thermistor resistance tests need a meter and temperature references.
- Reprogramming temperature settings is a service menu task.
- The tank area is hot and wiring is at line voltage.
How error code Er2 differs from similar codes
Er2 and Er3 share the same thermistor meaning in this manual revision; Er1 is the water fill 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 Er2 different from Er3?
In this manual revision the description is the same.
Is the water boiling?
It can be. The manual lists open, shorted or boiling.
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 Er2?
A technician confirms the cause on site and gives you the price in writing before any work starts.