Thermostat displays E19 and reports Wi-Fi security or authentication error.

Safety first: No internal electrical work is required for this fault.

• Step 1 – Re-enter credentials: On the thermostat, forget the current Wi-Fi network and re-add it, carefully entering the correct password (case-sensitive).
• Step 2 – Check router security: Ensure the router is using a supported security mode (typically WPA2-PSK). Avoid enterprise or WPA3-only modes if not supported by the thermostat.
• Step 3 – Disable MAC filtering: If your router uses MAC address filtering, add the thermostat’s MAC address to the allowed list or temporarily disable filtering.
• Step 4 – Reduce network complexity: If you have multiple SSIDs or mesh nodes, connect the thermostat to a simple 2.4 GHz SSID with a standard password to test.
• Step 5 – Firmware update: If you can temporarily connect via a different network (e.g., mobile hotspot), update the thermostat firmware to improve Wi-Fi compatibility.