BoilerFaultCodesVaillant d.00 Fault Code
Also written as D00 — same fault.
The Vaillant d.00 fault code means: your boiler is simply displaying a status message telling you it is automatically adjusting its power output to best heat your home, rather than indicating a fault.. It appears on 22 Vaillant models in our database.
Technical description: Heating maximum output: The maximum heating output varies depending on the product. Automatic: Unit automatically adjusts the maximum output to the current system demand
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.00 fault code
Click a model for the full fault code list and model-specific repair notes.
- aquaPLUS
- ecoFIT pure Repair: £0-90
- ecoFIT Pure 412
- ecoFIT Pure 418 Repair: £0-80
- ecoFIT Pure 425 Repair: £80-120
- ecoFIT Pure 435 Repair: £0-80
- ecoFIT Pure 835 Repair: £80-120
- 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.00 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