Vaillant smart thermostat shows large temperature swings, with the room alternately too hot and too cold.

Safety: No electrical work required.

• 1. Check thermostat location: Ensure it is on an interior wall, away from radiators, windows, and draughts. Relocate if necessary.
• 2. Review control settings: In the Vaillant controller menu, select the recommended control mode for your boiler (eBUS modulating where supported) and adjust hysteresis or cycle rate if available.
• 3. Smooth schedules: Avoid large, sudden setpoint changes. Use smaller setbacks and gradual transitions.
• 4. Adjust heating curve: For weather‑compensated systems, slightly lower the heating curve to reduce overshoot.
• 5. Monitor performance: Make one change at a time and observe for 24–48 hours before further adjustments.