BoilerFaultCodesVaillant d.36 Fault Code
Also written as D36 — same fault.
The Vaillant d.36 fault code means: your boiler is struggling to accurately detect or manage the rate at which water is flowing through the system, which may result in inconsistent water temperatures.. It appears on 17 Vaillant models in our database.
Technical description: Value for the hot water flow
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Vaillant models that show the d.36 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £120-210
- ecoFIT Pure 418 Repair: £150-250
- ecoFIT Pure 425 Repair: £150-250
- ecoFIT Pure 435 Repair: £120-250
- ecoFIT Pure 825 Repair: £120-220
- ecoFIT Pure 830 Repair: £120-250
- ecoFIT Pure 835 Repair: £150-250
- ecoTEC Plus 615
- ecoTEC Plus 620
- ecoTEC Plus 625
- ecoTEC Plus 630
- ecoTEC Plus 635
- ecoTEC Plus 840
- ecoTEC Pro / ecoTEC Plus
- ecoTEC sustain
- Home Combi Repair: £150-250
- Home System
Source
Vaillant d.36 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 ecoTEC Plus 840 manual (PDF)
- Vaillant ecoTEC Pro / ecoTEC Plus manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026