How much does it cost to fix Vaillant error code D.93?

Typical repair cost for the Vaillant D.93 fault is £90-180 including labour.

D.93 High

Vaillant D.93 Fault Code

Q: What does the Vaillant D.93 fault code mean?

Your boiler’s computer is confused about which specific model it is supposed to be, usually happening after a major part has been replaced.

Also written as D93 — same fault.

The Vaillant D.93 fault code means: your boiler’s computer is confused about which specific model it is supposed to be, usually happening after a major part has been replaced.. It appears on 5 Vaillant models in our database.

Technical description: DSN appliance variant setting

What causes the Vaillant D.93 fault?

This fault occurs when the boiler's main control board has lost its identity and doesn't know which power output or model size it is controlling. It most frequently happens after a new circuit board has been installed but hasn't been programmed with the correct device specific number. Without this data, the boiler stays in a safety mode because it doesn't know how much gas to burn or how fast to run the internal components.

Typical repair cost £90-180 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Vaillant models that show the D.93 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant D.93 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