E04 on display and no water flow is detected during service even when taps are open.

Safety: Shut off water supply and relieve pressure by opening a nearby tap before removing any flow components.

• Check actual flow: Confirm that there is water supply to the softener by placing it in bypass and opening a faucet. If no water, the issue is upstream plumbing, not the softener.
• Inspect flow sensor: Locate the Hansgrohe flow sensor (often integrated in the inlet or valve body). Disconnect its wiring harness and check for corrosion or loose pins. Clean and reconnect.
• Clean turbine: Remove the flow sensor or turbine cartridge from its housing. Rinse under running water to remove debris, sand, or scale. Ensure the turbine spins freely with a gentle puff of air.
• Check wiring continuity: With power off, use a multimeter to verify continuity of the flow sensor wires from the sensor plug to the main control board connector.
• Reinstall and test: Reassemble the flow sensor, restore water and power, and run water through the system. Watch the display for flow indication. If E04 remains, the flow sensor module should be replaced.