BoilerFaultCodesVaillant D.96 Fault Code
Also written as D96 — same fault.
The Vaillant D.96 fault code means: your boiler has lost its unique configuration settings and currently thinks it is a blank unit from the factory.. It appears on 5 Vaillant models in our database.
Technical description: Factory setting
What causes the Vaillant D.96 fault?
This fault occurs when the boiler's internal memory has been wiped or corrupted, meaning the unit has forgotten its specific model and power settings. It is usually caused by a major electrical surge or a failure in the main control board that erases the vital 'Device Specific Number' needed for operation. Without this digital identity, the boiler shuts down as a safety precaution because it no longer knows how to manage its gas and water flow safely.
This fault is more common during winter or stormy weather, as power surges and lightning strikes are more frequent and can damage the boiler's sensitive electronic components.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Vaillant models that show the D.96 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant D.96 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026