The thermostat shows a room temperature that is clearly inaccurate (e.g., 5–10°C off compared to other thermometers).

Safety: No mains work required for basic checks.

• Compare readings: Place a reliable thermometer near the thermostat and compare readings after 30 minutes.
• Clear vents: Ensure the thermostat's front and side vents are not blocked by paint, wallpaper, or covers.
• Check mounting: Avoid mounting on external walls or above radiators. If necessary, relocate to an internal wall.
• Offset setting: Some Saunier Duval thermostats allow a temperature offset in the settings; adjust by the measured difference.

If large errors persist even after relocation and offset, the internal sensor is likely faulty, and the thermostat should be replaced.