BoilerFaultCodesViessmann 63:15 Fault Code
Also written as 6315 — same fault.
The Viessmann 63:15 fault code means: your boiler has detected an internal electronic error that suggests the main control unit is beginning to fail, which may cause your heating and hot water to become unreliable.. It appears on 5 Viessmann models in our database.
Technical description: 2x daily
What causes the Viessmann 63:15 fault?
This fault occurs when the boiler's internal computer brain fails to perform its routine self-checks correctly. It is typically caused by aging electronic components on the circuit board that can no longer communicate reliably with the rest of the system. While the boiler may occasionally clear the error on its own, it usually indicates that the hardware is worn out and needs professional attention.
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 63:15 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 63:15 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