F06 displayed and the softener does not regenerate at the programmed time

Safety: No internal high‑voltage work is required for basic checks, but disconnect power before removing the control panel cover.

Steps:

• Check programming: Enter the programming menu and verify the current time, hardness setting, and regeneration schedule. Correct any obvious errors.
• Power cycle: Turn the unit off for 1–2 minutes, then restore power. Re‑enter the time and date if prompted.
• Inspect backup battery: Some Vaillant control boards use a coin‑cell or small rechargeable battery to maintain the clock. If accessible, check for corrosion or leakage and replace with the exact specified type.
• Monitor for drift: After reprogramming, check the clock after 24–48 hours. If it loses time or resets, the RTC circuit or PCB is likely defective.
• Manual regeneration: Until the fault is resolved, you can trigger manual regenerations according to water usage to maintain softening performance.

Note: If F06 persists after battery replacement and reprogramming, the control PCB will usually need replacement by a qualified technician.