Display shows F1 and softener does not regenerate automatically

Safety first: Isolate the softener from mains power and close the inlet valve before opening any covers. Depressurize by opening a nearby tap.

• Check water flow: Open a tap and confirm there is actual water flow through the softener. If no flow, check inlet valve, pre-filter, and any shut-off valves.
• Inspect flow sensor wiring: Remove the front cover of the Viessmann softener. Locate the flow sensor (usually installed on the inlet or outlet manifold). Verify the plug is fully seated on the control board and that the cable is not pinched or damaged.
• Clean the flow sensor: Shut off water, disconnect the flow sensor body, and inspect the turbine/impeller for debris, scale, or resin beads. Rinse with clean water; do not use sharp tools on the turbine.
• Test sensor operation: With power restored and water flowing, observe the display for flow indication (often a moving symbol or changing volume counter). If there is flow but no indication, the sensor is likely defective.
• Replace if needed: If cleaning and wiring checks do not clear F1, replace the Viessmann flow sensor assembly. If a new sensor does not resolve the issue, the control board input may be faulty and a technician should be called.