Thermostat display shows E01 and cannot connect to Wi‑Fi or Atlantic cloud services.

Safety first: This is a low‑voltage control device, but always switch off power to the HVAC system at the breaker before removing the thermostat from its wall plate.

• Step 1 – Reboot the thermostat: Remove the thermostat from the wall base (if it has a detachable front) or power it off from the menu. Wait 60 seconds, then power it back on and check if E01 clears.
• Step 2 – Reset network settings: In the Atlantic app or on the thermostat menu, navigate to Settings > Network > Reset Wi‑Fi. Re‑enter your 2.4 GHz SSID and password. Ensure the router is broadcasting 2.4 GHz (not 5 GHz only).
• Step 3 – Check router and internet: Confirm other devices can connect to the same Wi‑Fi. Disable router MAC filtering or access control lists temporarily. Ensure outbound ports 80 and 443 are not blocked for the thermostat.
• Step 4 – Inspect signal strength: If the thermostat is far from the router or behind thick walls, move the router closer or add a Wi‑Fi extender. Check the thermostat’s Wi‑Fi signal indicator; if it shows 1 bar or less, poor signal may trigger E01.
• Step 5 – Hardware inspection (advanced): With power off, remove the thermostat front cover and visually inspect the main control PCB for a small Wi‑Fi module (often a shielded RF can or ESP‑style module) and antenna lead. Look for cracked solder joints, burnt spots, or a detached antenna wire. Do not attempt micro‑soldering unless qualified.
• Step 6 – Firmware update: If you can briefly connect via mobile hotspot, use the Atlantic app to check for and install the latest firmware, which may resolve network stack issues.
• When to replace: If E01 persists on multiple known‑good networks and after reset, the Wi‑Fi module on the main PCB is likely defective and the thermostat front module or main PCB should be replaced.