E5 displayed and thermostat cannot communicate with the Danfoss Ally Gateway or app; remote control unavailable.

Safety first: No mains wiring is involved for battery thermostats, but avoid opening the housing beyond user‑accessible covers.

Steps:

• Check gateway status: Verify that the Danfoss Ally Gateway is powered, connected to the router, and shows normal status LEDs.
• Reduce distance and obstacles: Move the gateway closer to the thermostat or vice versa. Avoid placing the gateway inside metal cabinets or directly behind large appliances.
• Re‑pair the device: In the Ally app, remove the thermostat from the system, then put it into pairing mode and add it again as a new device.
• Check for RF interference: If many Wi‑Fi networks or Zigbee devices are nearby, change the Zigbee channel on the Ally Gateway (if supported) and reboot the gateway.
• Firmware update: Use the Ally app to check for and install firmware updates for both the gateway and thermostat.
• If E5 remains: The Zigbee radio on the thermostat PCB may be defective. Replace the thermostat unit.