Grindmaster Grind’n Brew Error Code Er4: Heater Error
Er4 is a heater error: the heater has been on for 3 minutes and no rise in water temperature was detected. Clear it by holding the UP key for 5 seconds, resetting power, or entering field test mode. A technician should check the heater relay, contactor and heater element.
High: water fill and heat shut off and brewing is disabled until the heater problem is fixed.
- Code
- Er4
- Maker
- Grindmaster
- Equipment
- Coffee brewers
- Applies to
- Grind'n Brew GNB-10H/11H/20H/21H
What does Grindmaster error code Er4 mean?
The control switches the heater on and watches the thermistor for a rise in water temperature. If the heater has been on for 3 minutes and the water has not warmed, the control shows Er4, a heater error. 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 manual's troubleshooting guide lists a failed heater relay, a failed contactor and a heater that has failed open. The remedy column also lists turning power or the switch on, checking the high-temperature failure and the control board output, and replacing the defective part. To clear the error, hold the UP key for 5 seconds, reset power to the unit, or enter field test mode. Clearing does not heat the water. If the heater circuit has failed, Er4 will come back after three minutes of heating every time.
Affected models and control systems
Grindmaster Grind'n Brew GNB-10H, GNB-11H, GNB-20H and GNB-21H.
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
- Er4 on the display when the unit is idle
- Basket Out light flashing
- Water not heating
- Grinding still works
Possible causes
Listed in Grindmaster's documentation
- Heater relay failed
- Contactor failed
- Heater failed open
Other likely causes — what usually sits behind error code Er4 on this control. A technician confirms which one it is before any part is replaced.
- High-temperature protection tripped and cutting the heater
- Control board output not driving the relay
- Loose terminal at the heater
Safe checks before calling for service
- Check that the power switch is on.
- Hold the UP key for 5 seconds, or switch the power off and on.
- Try one brew and see whether the water warms.
- If Er4 returns, note how long the brewer was on and call us.
How a technician diagnoses error code Er4
- Read the display and confirm Er4.
- Check the heater relay, contactor and heater element.
- Check the high-temperature protection.
- Check the control board output.
- Replace the part that fails.
- The heater circuit carries high current at line voltage.
- Relay and contactor tests need a meter with the unit isolated.
- The high-temperature protection must be understood before it is reset.
How error code Er4 differs from similar codes
Er4 is the heater error; Er2 and Er3 are thermistor errors, and 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
How long does the heater run before Er4?
The manual says 3 minutes without a temperature rise.
Is the thermistor involved?
It senses the rise, but Er4 points to the heater circuit.
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 Er4?
A technician confirms the cause on site and gives you the price in writing before any work starts.