Thermostat shows F.08 and app cannot access heating data

Safety: No electrical work is required. This is a network/service issue.

Checks:

• Confirm that the thermostat is connected to Wi‑Fi (no Wi‑Fi error present) and that internet access works on other devices.
• Check Glow‑worm or Vaillant group service status pages or support channels for any reported cloud outages.
• Restart the router and thermostat to refresh IP and DNS settings.
• Ensure your router is not blocking outbound HTTPS traffic or using overly strict parental controls that might block the thermostat.
• If the thermostat firmware can be updated locally, apply the latest firmware version as recommended by Glow‑worm.

Remedy:

• If the error only occurs intermittently and clears on its own, it is likely a temporary cloud issue.
• If F.08 is permanent while all other internet services work, contact Glow‑worm technical support; they may need to check the device registration or replace the thermostat/gateway if its cloud client is corrupted.