Thermostat displays E19 and may not complete initial setup or may lose configuration after power cycles.

Safety first: No high-voltage work is required; do not open the thermostat housing.

• Step 1 – Stable power: Ensure the HVAC breakers are not tripping and that the thermostat has a stable 24 VAC supply.
• Step 2 – Factory reset: Access the thermostat's advanced settings and perform a full factory reset. Re-run the guided setup for your Carrier system.
• Step 3 – Firmware update: Connect the thermostat to Wi‑Fi and check for firmware updates. Apply any available updates and allow the thermostat to reboot fully.
• Step 4 – Avoid interruptions: During setup and updates, do not cut power or remove the thermostat from the wall plate.
• Step 5 – Replace thermostat: If E19 recurs after reset and update, the internal memory is likely defective and the thermostat should be replaced.
• When to call a pro: A technician can confirm that the issue is not caused by external control wiring or equipment faults.