Wiser Room Thermostat displays E02 and does not measure room temperature correctly; heating does not respond.

Safety: The room thermostat is battery powered and low voltage. Do not attempt to open the casing beyond the normal battery compartment; internal repairs should be done by a professional or via replacement.

• Power-cycle the thermostat: Remove both batteries, wait 30 seconds, and reinstall fresh, good-quality alkaline batteries. Allow the thermostat to reboot and check if E02 clears.
• Check location and environment: Ensure the thermostat is not installed above a radiator, in direct sunlight, or near a draught. Excess heat or cold can trigger sensor protection or make the error appear intermittent.
• Inspect for condensation or damage: Look for signs of moisture, staining, or physical damage to the thermostat housing. If the thermostat has been exposed to water or heavy condensation, the internal sensor may be permanently damaged.
• Compare temperature reading: If the error clears but readings are obviously wrong compared to a reliable thermometer, the internal NTC sensor is likely out of tolerance and the thermostat should be replaced.

If E02 persists after battery replacement and relocation, the internal sensor or PCB is faulty. Replace the Wiser Room Thermostat as a complete unit.