Thermostat displays E4 and will not complete Wi‑Fi setup

Safety: No high‑voltage work is required for this fault. Do not remove power to the HVAC unless you are also working on wiring.

Steps to resolve:

• Confirm network compatibility: Ensure your router is broadcasting a 2.4 GHz network with WPA2 or similar standard security. Many Sensi models do not support 5 GHz‑only networks.
• Improve signal strength: Temporarily move your Wi‑Fi router closer to the thermostat or use a Wi‑Fi extender. Thick walls, metal ductwork, and appliances can weaken the signal.
• Reset Wi‑Fi on thermostat: Use the Sensi app or on‑screen menu to forget the current network and start a fresh Wi‑Fi setup. Follow the Sensi pairing instructions exactly, including any temporary Sensi‑xxxx network steps.
• Check router settings: Disable MAC address filtering or add the thermostat's MAC address to the allowed list. Ensure the router is not blocking new devices or using enterprise authentication methods unsupported by Sensi.
• Firmware update: If the thermostat has ever connected before, check in the Sensi app for firmware updates. A router firmware update can also resolve compatibility issues.

When to replace: If multiple known‑good networks fail and other devices connect normally, the Wi‑Fi radio on the thermostat may be defective. In that case, replacing the thermostat is typically required.