E08 error and thermostat reports humidity as “--” or 0%/99% constantly

Safety: Turn off power to the HVAC system before removing the thermostat from the wall.

• Step 1 – Reboot and reset:
  • Power cycle the thermostat at the breaker.
  • If E08 remains, perform a factory reset from the settings menu.
• Step 2 – Check environment:
  • Ensure the thermostat is not installed in a bathroom, above a humidifier outlet, or where steam regularly contacts the device.
  • Do not spray cleaners directly on the thermostat; wipe with a dry or slightly damp cloth only.
• Step 3 – Inspect humidity sensor (advanced):
  • Remove the thermostat from the wall plate.
  • Locate the small humidity sensor IC on the PCB (often a small vented package near air slots).
  • Check for corrosion, residue, or physical damage.
• Step 4 – Replace thermostat if sensor is defective:
  • The humidity sensor is surface‑mounted and not user‑replaceable.
  • If E08 persists after reset and cleaning, replace the thermostat.