Thermostat shows much higher or lower temperature than actual room temperature.

Safety first: Isolate mains before removing a wired thermostat from the wall.

• Seal wall penetration: Remove the thermostat and seal any large cable holes in the wall with non-conductive filler to prevent draughts.
• Check mounting surface: Avoid mounting on cold external walls or above concealed pipes. Relocate to an internal wall if necessary.
• Compare with reference: Use a reliable thermometer to determine the actual room temperature and apply a calibration offset in the thermostat settings if available.
• Replace thermostat: If readings remain unstable or significantly wrong, replace the thermostat front module to renew the sensor.