Thermostat shows a much higher or lower temperature than the actual room temperature by a consistent offset.

Safety first: No hazardous work required.

Steps:

• Compare with reference: Place a reliable thermometer near the thermostat and compare readings after 30 minutes.
• Adjust offset: If supported, use the Ally app or thermostat installer menu to apply a temperature offset to match the reference.
• Improve location: If the thermostat is on an exterior wall or near a draught, relocate it to a more representative position.
• Replace if extreme: If the offset is very large (>5°C) and cannot be corrected, the sensor may be defective; replace the thermostat.