BoilerFaultCodesZanussi dU Fault Code
Also written as DU — same fault.
The Zanussi dU fault code means: your boiler is not broken; it is simply in a special service mode used by engineers when they are preparing to replace internal parts.. It appears on 1 Zanussi model in our database.
Technical description: To move the diverter valve to mid-position for replacement
What causes the Zanussi dU fault?
This code appears when someone has manually activated the diverter valve service function, usually by pressing a specific combination of buttons. It is a programmed setting that moves internal components into a neutral position to allow an engineer to safely drain the unit and replace parts. It is not caused by a mechanical failure but by the boiler being placed into a pre-service state.
DIY fix possible
Turn the mains power to the boiler offWait 30 secondsTurn the power back on to reset the boiler to normal operation
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Zanussi models that show the dU fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Zanussi dU fault code information on this page is sourced and cross-checked against the official Zanussi service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026