Wiser Room Thermostat shows E03 and the display is frozen or unresponsive to button presses.

Safety: The thermostat is low voltage. Do not attempt board-level repair.

• Hard reset via batteries: Remove all batteries from the thermostat. Press any button for 10 seconds to discharge residual power. Wait 1 minute, then insert new alkaline batteries, observing polarity.
• Check for stuck buttons: Gently press each button several times to ensure none are physically stuck. Dirt or debris can cause constant keypress detection and lock the interface.
• Rejoin to system: If the thermostat restarts without E03 but does not control heating, remove it from the Wiser app and re-add it as a new device.
• Check battery contacts: Ensure the spring contacts in the battery compartment are clean and not bent. Lightly clean with a dry cloth if corroded; do not use liquids.

If E03 reappears frequently, the thermostat's MCU or firmware is likely defective. Replace the thermostat assembly.