BoilerFaultCodesViessmann 6F:100 Fault Code
Also written as 6F100 — same fault.
The Viessmann 6F:100 fault code means: your boiler is telling you that it has defaulted to its maximum power setting for heating your hot water because it has encountered a configuration memory error.. It appears on 5 Viessmann models in our database.
Technical description: Max. output during DHW loading 100%, defaulted by the boiler coding card
What causes the Viessmann 6F:100 fault?
This fault occurs because the boiler's internal memory chip, which stores its specific performance settings, has failed or lost communication with the main computer. Without these specific instructions, the boiler enters a 'safe mode' where it lacks the data to modulate its power, leading it to default to maximum output when heating your water. It is usually caused by a physical hardware failure in the coding card or a fault on the main control board.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Viessmann models that show the 6F:100 fault code
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Source
Viessmann 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