BoilerFaultCodesVaillant D,11 Fault Code
Also written as D11 — same fault.
The Vaillant D,11 fault code means: your boiler is struggling to push hot water around your radiators because an external pump is not responding correctly.. It appears on 38 Vaillant models in our database.
Technical description: Status external heating pump error
What causes the Vaillant D,11 fault?
This fault occurs when the boiler sends a signal to an external pump but does not receive the necessary feedback to confirm it is working. The most common reasons are a mechanical failure within the pump itself, a loose connection in the wiring, or a communication error within the main control board. Without this pump operating correctly, the boiler cannot safely move heat away from its internal heat exchanger.
This fault is more common in autumn when heating systems are switched back on after being idle all summer, which can cause external pumps to seize.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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Vaillant models that show the D,11 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £180-£350
- ecoFIT Pure 418 Repair: £0-120
- ecoFIT Pure 425
- ecoFIT Pure 435
- ecoFIT Pure 825 Repair: £120-250
- ecoFIT Pure 830 Repair: £150-350
- ecoFIT Pure 835
- ecoMAX Repair: £150-300
- ecoMAX 613 Repair: £150-300
- ecoMAX 618 Repair: £150-350
- ecoMAX 622 Repair: £150-300
- ecoMAX 635 Repair: £150-300
- ecoMAX 824E Repair: £120-250
- ecoMAX 828E Repair: £150-300
- Ecomax Condensing 600/800 series Repair: £150-300
- ecoMAX System 612 Repair: £150-300
- ecoTEC Repair: £180-350
- ecoTEC 65kW
- ecoTEC Plus 610 Repair: £180-350
- ecoTEC Plus 615 Repair: £150-300
- ecoTEC Plus 620 Repair: £150-300
- ecoTEC Plus 625 Repair: £150-300
- ecoTEC Plus 630 Repair: £150-300
- ecoTEC Plus 635 Repair: £150-300
- ecoTEC Plus 840 Repair: £150-300
- ecoTEC plus aquaPLUS Repair: £180-350
- ecoTEC Pro / ecoTEC Plus
- ecoTEC sustain Repair: £150-300
- Home Combi Repair: £150-300
- Home System
- Thermocompact
- Turbomax 824/828 Repair: £150-300
- Turbomax Plus Repair: £120-250
- Turbomax Plus 824/828E Repair: £150-300
- Turbomax Plus 828 Repair: £100-250
- Turbomax Plus 828 E
- Turbomax Plus VUW 242E
- Turbomax Plus VUW 242EH
Source
Vaillant D,11 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
- Vaillant ecoFIT Pure 835 manual (PDF)
- Vaillant ecoMAX manual (PDF)
- Vaillant ecoMAX System 612 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026