Safety: Turn off power and close the inlet valve before removing any flow components.

Steps:

Confirm actual water flow: Open a tap downstream of the softener. If water flows normally but the display shows zero consumption, the issue is with the flow measurement system.
Remove and inspect flow meter: The flow meter is typically integrated into the inlet block. Remove it according to the service manual. Check the turbine wheel for scale, sand, or debris. It should spin freely with a gentle puff of air.
Clean and descale: Soak the turbine and housing in a mild descaler (citric acid or white vinegar), then rinse thoroughly. Do not scratch the surfaces.
Check electrical connection: Inspect the Hall sensor connector and cable for damage or corrosion. Reseat the connector on the control board.
Test sensor: With a multimeter (if competent), verify that the Hall sensor receives supply voltage and produces pulses when the turbine is rotated. Replace the flow meter assembly if no pulses are generated.
Reassemble and reset: Refit the flow meter, restore water and power, clear the F04 code, and verify that flow is now registered on the display.

F04 displayed and no water flow is registered even when taps are open

Possible Causes