Display shows F6 and unit does not count down remaining capacity correctly

Safety first: Ensure the unit is powered but do not open any pressurized components.

• Verify programming: Enter the installer menu on the Viessmann controller and confirm that the raw water hardness and resin capacity are set according to the commissioning sheet.
• Check flow sensor orientation: Inspect the flow sensor body for an arrow indicating flow direction. Ensure it matches the actual water flow through the softener.
• Reset controller: Perform a soft reset according to the user manual (often by disconnecting power for several minutes). Re-enter settings if required.
• Test volume counting: Run water through the system and observe the display. The remaining capacity should decrease as water is used. If it does not, the flow meter may be defective.
• Replace if needed: Install a new Viessmann flow meter / sensor if calibration cannot be corrected and F6 persists.