Display shows F3 and unit remains in service mode without regenerating

Safety first: Disconnect power before removing the valve head cover. Close inlet and outlet valves and open a tap to relieve pressure.

• Listen for motor operation: Restore power and initiate a manual regeneration. Listen for the valve motor. A humming or no sound at all may indicate a stuck or failed motor.
• Inspect valve head: Remove the plastic cover on the valve head. Check for visible damage, broken gears, or loose motor mounting screws.
• Check for mechanical blockage: With power off, gently attempt to rotate the valve cam (if accessible) by hand according to the service manual. If it will not move, the rotary valve may be jammed by debris or scale.
• Verify motor wiring: Ensure the motor connector is firmly seated on the control board and that wires are not damaged.
• Replace components as needed: If the valve is free but the motor does not run, replace the Viessmann valve motor assembly. If a new motor does not resolve F3, the control board may be defective and should be serviced by a qualified technician.