BoilerFaultCodesViessmann 7b:1 Fault Code
Also written as 7B1 — same fault.
The Viessmann 7b:1 fault code means: your boiler is having a minor communication issue where it cannot sync its internal clock with other connected heating components.. It appears on 5 Viessmann models in our database.
Technical description: Send time to LON
What causes the Viessmann 7b:1 fault?
This fault occurs when the boiler's internal control board fails to transmit the current time and date across the communication network to other system components. It is almost always caused by a software configuration error or a conflict in the settings between the boiler and an external control module. Because it is a data sync issue rather than a mechanical failure, it rarely requires physical parts to be replaced.
DIY fix possible
Locate the main control panel and access the Menu.Go to Settings and find the Date/Time option.Manually reset the time and date to ensure the system updates its internal clock.
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Gas Safe Register →Viessmann models that show the 7b:1 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 7b:1 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026