Thermostat displays E09 and cannot connect to cloud services or voice assistants despite being on Wi‑Fi.

Safety first: No high-voltage work is needed for this fault.

Steps to troubleshoot:

• Verify internet access: Confirm other devices on the same Wi‑Fi network can access the internet.
• Check router firewall: Ensure outbound HTTPS (port 443) is allowed and that no parental controls or firewall rules are blocking the thermostat’s MAC address.
• Reboot router and thermostat: Power cycle the router, then turn the thermostat breaker OFF for 2 minutes and back ON.
• Re-link integrations: In the Mysa app, sign out and back in, then re-link any smart home integrations (Alexa, Google, HomeKit) if needed.
• Factory reset as last resort: If E09 persists, perform a factory reset on the thermostat and set it up again from scratch.

If the thermostat connects to Wi‑Fi but never reaches the cloud after all network checks, the internal TLS/communication stack on the main board may be corrupted. Replacement may be required.