Display shows E04 and regeneration cannot be started

Safety: Disconnect the appliance from mains power before opening the valve head.

• Listen for motor: When attempting regeneration (briefly reconnect power), listen for the drive motor. A humming sound without movement suggests a jammed gear or piston.
• Inspect drive assembly: Remove the control cover to access the motor and gear train. Check for broken teeth, foreign objects, or misaligned gears. Clean and re-grease with a suitable food-grade lubricant if necessary.
• Check position sensor: Many Grünbeck heads use a cam and microswitch or encoder. Verify the connector is seated and the cam is not loose. Test the switch with a multimeter for proper switching.
• Free seized piston: If the main valve piston is stuck due to scale, carefully remove it according to the service instructions, descale with a manufacturer-approved descaling agent, rinse thoroughly, and reinstall with new seals if worn.
• Re-test: Reassemble, restore power, and start a manual regeneration to confirm the error is cleared. If the motor does not run at all, replace the drive motor assembly.