Display shows 'Lo' or a low salt icon, and an audible alarm sounds.

Safety first: No electrical or hydraulic work is needed; keep the unit powered.

• Refill salt: Open the brine tank and add the recommended type of salt (Viessmann-approved tablet or block salt) up to the indicated level.
• Check for salt bridge: Use a plastic rod to gently probe the salt. If you feel a hollow space under a hard crust, break the bridge and remove loose chunks.
• Reset alarm: After refilling, acknowledge or reset the low salt warning via the control panel.
• Sensor check: If 'Lo' remains despite adequate salt, clean the salt level sensor and verify its wiring. Replace the Viessmann salt level sensor if necessary.