B8
Viessmann
Firmware Update Failure
Thermostat shows B8 and cannot complete a firmware update; device may reboot repeatedly.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Interrupted internet connection during update, Insufficient power or battery during update, Corrupted firmware file, Incompatible firmware version pushed to device
How to Fix / Troubleshooting
Safety first: Do not remove power during an active firmware update unless instructed by support.
- Stabilize power: Ensure the thermostat has stable power (fresh batteries or reliable mains supply) before retrying the update.
- Check internet connection: Verify that the network is stable and has good bandwidth.
- Retry update: Use the Viessmann app to manually trigger the firmware update again if the option is available.
- Factory reset (if stuck): If the thermostat is stuck in a reboot loop and the manual allows, perform a hardware reset according to the instructions.
- Contact Viessmann support: If B8 persists, support may need to push a recovery firmware or replace the device.
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Repair Difficulty
Medium
3/5
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