Display shows 'Hi' or maximum temperature; thermostat may stop heating control for safety.

Safety first: If the room is genuinely very hot, ventilate the area and investigate the heating system for runaway operation.

Steps:

• Check actual room temperature: Use a separate thermometer to confirm whether the room is truly overheated.
• Inspect mounting location: If the thermostat is above a radiator, near a hot pipe, or in direct sunlight, relocate it to an interior wall at about 1.5 m height away from heat sources.
• Allow to cool: Turn down the setpoint or switch off heating temporarily and allow the thermostat to cool to normal room temperature.
• Reset device: Power cycle or factory reset the thermostat if it continues to show 'Hi' at normal room temperature. If the error persists, the internal sensor may be defective and the thermostat should be replaced.