BoilerFaultCodesVaillant d.01 Fault Code
Also written as D01 — same fault.
The Vaillant d.01 fault code means: your boiler is currently running its internal pump to move excess heat away from the system, which is a normal part of the cooling-down process after your heating or hot water has been active.. It appears on 22 Vaillant models in our database.
Technical description: Water pump over run
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Vaillant models that show the d.01 fault code
Click a model for the full fault code list and model-specific repair notes.
- aquaPLUS
- ecoFIT pure
- ecoFIT Pure 412
- ecoFIT Pure 418
- ecoFIT Pure 425
- ecoFIT Pure 435
- ecoFIT Pure 835
- ecoTEC plus
- ecoTEC Plus 615
- ecoTEC Plus 620
- ecoTEC Plus 625
- ecoTEC Plus 630
- ecoTEC Plus 635
- ecoTEC Plus 65
- ecoTEC Plus 832
- ecoTEC Plus 836
- ecoTEC Plus 840
- ecoTEC Plus 938
- ecoTEC plus Aquaplus
- ecoTEC plus System
- ecoTEC sustain
- Home System
Source
Vaillant d.01 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