Thermostat shows E3 and reports incorrect room temperature

Safety first: Turn off power at the breaker before removing the thermostat from the wall.

Steps to troubleshoot E3 (internal sensor fault):

• 1. Check installation location:
  • Ensure the thermostat is not installed above a radiator, in direct sunlight, or near other heat sources.
  • Excessive heat can damage the internal sensor and cause error codes.
• 2. Power cycle the thermostat:
  • Turn off the breaker for 2–3 minutes.
  • Restore power and check if E3 clears.
• 3. Inspect for physical damage:
  • Remove the thermostat from the backplate.
  • Look for signs of burning, discoloration, or liquid damage on the PCB and around the small internal sensor component.
• 4. Update firmware:
  • Use the Fibaro Home Center or compatible Z‑Wave hub to check for thermostat firmware updates.
  • Apply any available updates, then reboot the device.
• 5. Replace the thermostat if sensor is defective:
  • The internal air sensor is typically integrated on the PCB and not user-replaceable.
  • If E3 persists after power cycling and firmware update, the thermostat module should be replaced.

When to call a professional: If you are not comfortable working around mains wiring or the thermostat shows signs of overheating or burning, contact a licensed electrician or HVAC technician to replace the unit.