Thermostat display shows E01 and will not connect to Wi‑Fi or Johnson Controls cloud services.

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

• Step 1 – Reboot the thermostat: Turn off HVAC power at the breaker for 60 seconds, then restore power. Wait 3–5 minutes to see if E01 clears.
• Step 2 – Reset network settings: From the thermostat menu, navigate to Settings > Network > Reset Network. Re‑enter your Wi‑Fi SSID and password. Confirm the router is broadcasting 2.4 GHz if required by your model.
• Step 3 – Check router distance and interference: Ensure the thermostat is within 20–30 ft of the router with minimal walls/metal between. Temporarily power off nearby RF devices (microwave, cordless phones, baby monitors) and test again.
• Step 4 – Inspect antenna connection: With power off, gently pull the thermostat off the wall sub‑base. Inspect the small Wi‑Fi antenna lead or PCB antenna on the main control board for obvious damage or loose connectors. Do not short any components.
• Step 5 – Firmware update: If you can briefly connect via mobile hotspot, check the Johnson Controls app or web portal for a firmware update and apply it.
• Step 6 – Replace control module: If E01 persists and other devices connect fine to Wi‑Fi, the Wi‑Fi radio on the main control board is likely failed. Replace the thermostat main control board / display module or the entire thermostat assembly. This is usually best done by a qualified technician to avoid damaging low‑voltage wiring.