Thermostat shows E02 and does not control heating correctly; temperature reading may be frozen or missing.

Safety first: For battery-powered Delta Dore thermostats, remove batteries before opening the housing. For mains-powered models, isolate power at the breaker before any disassembly.

• Power cycle the thermostat: Remove the thermostat from its wall plate, take out the batteries (if applicable) or switch off power for 2–3 minutes, then restore power. Check if E02 clears.
• Inspect for condensation or moisture: Open the front cover and look for signs of moisture, corrosion, or dust on the sensor area (usually a small component near the air vents). Gently clean with a dry, soft brush. Do not use liquids.
• Check installation location: Ensure the thermostat is not installed directly above a radiator, in direct sunlight, or on an external cold wall. Excess heat or cold can stress the sensor and cause intermittent E02. Relocate if necessary.
• Reset to factory settings: Use the menu: Menu > Settings > Reset / Factory reset (exact path may vary by model) and reconfigure. If E02 remains, the internal NTC sensor on the PCB is likely faulty.

Internal sensors on Delta Dore smart thermostats are not usually user-replaceable; replacing the complete thermostat head or main PCB is typically required and should be done by a professional.