Smart thermostat shows F.02 and cannot detect the boiler; no heating control via app or room unit.

Safety: Isolate mains power to the boiler and any wiring centers before opening covers.

• 1. Confirm boiler supports eBUS: Check the boiler model (e.g. ecoTEC, ecoFIT, ecoTEC plus) and verify it has eBUS terminals. Older models may require a specific Vaillant controller or adapter.
• 2. Check wiring at boiler: Remove the boiler front panel as per the manual. Locate the eBUS terminals (often marked 7/8 or eBUS). Ensure the thermostat cable is firmly connected and not mixed with 230 V terminals.
• 3. Remove other controls: If there is an external 3rd‑party controller or weather compensator on the same bus, temporarily disconnect it and leave only the Vaillant smart thermostat connected. Restore power and see if F.02 clears.
• 4. Inspect for damage: Look for burn marks or corrosion on the boiler’s eBUS connector or PCB. If visible damage is present, do not attempt board repair yourself; call a qualified engineer.
• 5. Reset system: Power down boiler and thermostat for 2–3 minutes, then power up the boiler first, then the thermostat. Allow a few minutes for bus negotiation.
• 6. If F.02 persists: The boiler’s eBUS board or the thermostat may be defective. A Vaillant service technician should test bus voltage and replace the faulty module.