Thermostat displays E20 and indicates a sensor calibration or configuration mismatch after a firmware update.

Safety first: No high‑voltage work is required.

• Step 1 – Reboot thermostat: Remove the thermostat from the wall plate for 30 seconds, then reattach. Check if E20 clears.
• Step 2 – Reapply firmware update: Using the Geo app, attempt to reinstall the latest firmware version, ensuring a stable Wi‑Fi connection.
• Step 3 – Factory reset: Perform a full factory reset from the settings menu. This will erase schedules and custom settings but can restore default calibration data.
• Step 4 – Reconfigure sensors: After reset, reconfigure any remote or outdoor sensors and verify their readings.
• Step 5 – Replace thermostat: If E20 persists after reset and reconfiguration, the non‑volatile memory storing calibration data may be defective. Replace the thermostat head unit.