Wiser Room Thermostat shows E13 and the app indicates under-temperature or frost protection error.

Safety: No mains work required.

• Check location: Ensure the thermostat is installed in a normally heated room, not in a loft, porch, or external wall box.
• Allow to warm: If the thermostat has been stored in a very cold environment, bring it to room temperature and wait 30 minutes.
• Battery reset: Remove and reinstall batteries to clear the error.

If E13 persists at normal room temperature, the internal sensor is likely defective. Replace the thermostat.