Vaillant smart thermostat shows F.13 and one or more wireless room units frequently drop offline.

Safety: Only low‑voltage/battery work; no mains exposure if you avoid boiler internals.

• 1. Replace batteries: In battery‑powered Vaillant room units, fit fresh high‑quality alkaline batteries and ensure correct polarity.
• 2. Reposition devices: Move the thermostat or receiver away from large metal objects, fridges, or consumer units. Try to maintain line‑of‑sight or reduce the number of walls between devices.
• 3. Reduce interference: Keep Wi‑Fi routers, cordless phone bases, and baby monitors at least 1–2 m away from the thermostat/receiver.
• 4. Re‑pair devices: Delete and re‑pair the affected wireless units via the controller menu, following Vaillant’s pairing procedure.
• 5. Test with a single unit: Temporarily operate with only one wireless room unit to rule out address conflicts.
• 6. Replace faulty RF module: If dropouts persist in good signal conditions, the RF module in the thermostat or receiver may be defective and should be replaced.