Thermostat shows E02 and does not control heating correctly

Safety first: Do not open the thermostat if you are not comfortable working with electronics. The thermostat itself is low voltage, but it may be mounted near mains wiring. Isolate power to the heating system before removing any backplate that carries mains.

• Reboot the thermostat: Remove the thermostat from its wall plate or remove batteries (if battery powered) for 30–60 seconds, then refit. Wait a few minutes to see if E02 clears.
• Check ambient conditions: Ensure the thermostat is not exposed to direct sunlight, draughts, or a heat source that could cause extreme readings. While this usually won’t trigger E02, it can help rule out environmental issues.
• Inspect for moisture: If the thermostat is in a humid area (e.g. near a bathroom), check for condensation on or behind the unit. If present, gently dry the area and allow the thermostat to acclimatise.
• Factory reset: Use the Wiser app or thermostat menu to perform a factory reset (note: you will need to reconfigure schedules). After reset, check if the error returns.
• If E02 remains: The internal NTC sensor on the thermostat PCB is likely defective. This is not user-serviceable; replace the thermostat head with a compatible Wiser Room Thermostat.