BoilerFaultCodesVaillant D.30 Fault Code
Also written as D30 — same fault.
The Vaillant D.30 fault code means: your boiler is struggling to send the correct message to its gas supply valves, which usually means it cannot light safely.. It appears on 7 Vaillant models in our database.
Technical description: Control signal for both gas valves
What causes the Vaillant D.30 fault?
This fault occurs when there is a communication failure between the boiler's main brain and the gas valves that let fuel into the burner. It is typically caused by a shortcut in the wiring or a failing circuit board that can no longer send the steady electronic signal required to keep the gas supply open. Because the boiler cannot confirm the gas valves are operating correctly, it shuts down immediately as a safety precaution.
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.30 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant D.30 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