BoilerFaultCodesViessmann 6F:0 to 6F:100 Fault Code
Also written as 6F0TO6F100 — same fault.
The Viessmann 6F:0 to 6F:100 fault code means: your boiler is providing an informational update about the maximum power level it is using to heat your hot water, rather than reporting a functional breakdown.. It appears on 5 Viessmann models in our database.
Technical description: Max. output during DHW loading adjustable from 0 to 100%
What causes the Viessmann 6F:0 to 6F:100 fault?
This notification occurs when the boiler is informing you that the maximum power output dedicated to heating your hot water has been manually adjusted or restricted. It is not a mechanical failure, but rather a configuration setting that tells the system how hard the burner should work when refilling your hot water cylinder. The most common reason for seeing this is following a recent service or setup change where the engineer has optimized the unit for energy efficiency.
DIY fix possible
No action is required as this is an advisory message indicating the power output setting.If hot water is too slow to heat, contact a professional to adjust the maximum output via the control unit.Restart the boiler to see if the notification clears from the display.
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Gas Safe Register →Viessmann models that show the 6F:0 to 6F:100 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 6F:0 to 6F:100 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