Display shows E04 and the unit stops mid‑regeneration, remaining in a fixed valve position.

Safety first: Isolate electrical power and turn the bypass valve to bypass position. Depressurise the system by opening a nearby tap.

• Listen for motor operation: With the cover removed, briefly restore power and attempt to start a manual regeneration. Listen for the valve motor. If it hums but does not turn, switch off immediately.
• Inspect valve rotor: Remove the control head cover and visually inspect the rotor and gear train. Look for broken teeth, misaligned gears, or foreign objects.
• Check wiring to motor and position switch: Ensure the motor connector and position sensor (microswitch or encoder) connectors are fully seated on the PCB.
• Manual indexing (if provided by model): Some Kinetico electronic heads allow manual rotation of the valve cam using a service tool. Gently rotate to the service position to free a jam, then re‑test.
• If E04 persists: The valve motor or position sensor is likely defective and the complete motor/gearbox assembly or control head may need replacement by a technician.

Warning: Do not force the valve rotor; excessive force can crack the control head casting and cause leaks.