Smart thermostat app or display shows 'No Signal' or cloud icon with a cross; remote control via app not working but local control may still function.

Safety first: This is a low‑voltage communication issue; no boiler isolation is normally required unless you are also working at the boiler. Do not open the boiler casing.

• Check internet and router: Confirm other devices can access the internet. Restart the router by powering it off for 30 seconds and back on.
• Check Wi‑Fi signal strength: Stand near the thermostat with a phone and check Wi‑Fi bars. If weak, move the router closer or add a Wi‑Fi extender.
• Re-enter Wi‑Fi details: On the thermostat, open the network settings, forget the current network, then reconnect by entering the correct SSID and password. Ensure you use a 2.4 GHz network if the thermostat does not support 5 GHz.
• Check app login: Log out and back into the Worcester Bosch / Bosch smart heating app. Ensure the account is verified and the device is still listed.
• Firmware update: If the thermostat menu shows a firmware update option, apply any pending updates while connected locally.
• If still failing: The Wi‑Fi module or main PCB in the thermostat may be defective. Contact Worcester Bosch support for diagnostics and possible replacement.