d.03 Low

Vaillant d.03 Fault Code

Also written as D03 — same fault.

The Vaillant d.03 fault code means: your boiler is currently showing you exactly how hot the water inside the storage tank is, rather than indicating a fault.. It appears on 1 Vaillant model in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Actual hot water temperature

DIY fix possible

Press the 'i' button to exit the diagnostic information modeWait for the display to automatically return to the standard pressure or temperature viewNo further action is required as this is a status information code, not an error

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Vaillant models that show the d.03 fault code

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

Source

Vaillant d.03 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 7 July 2026