BoilerFaultCodesVaillant D.64 Fault Code
Also written as D64 — same fault.
The Vaillant D.64 fault code means: your boiler is taking longer than usual to light, though it is still currently working.. It appears on 28 Vaillant models in our database.
Technical description: Average ignition times
What causes the Vaillant D.64 fault?
This issue occurs when the boiler's control board detects that the burner is taking a few seconds longer than normal to establish a stable flame. The most common reasons are worn-out spark electrodes that can no longer create a strong spark or a build-up of carbon deposits on the sensing probe which prevents it from 'seeing' the flame quickly.
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.64 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £90-250
- ecoFIT Pure 418 Repair: £100-250
- ecoFIT Pure 425 Repair: £80-200
- ecoFIT Pure 435 Repair: £100-250
- ecoFIT Pure 825 Repair: £120-250
- ecoFIT Pure 830 Repair: £120-250
- ecoFIT Pure 835 Repair: £100-250
- ecoTEC Repair: £100-250
- ecoTEC 65kW Repair: £150-300
- ecoTEC Plus 615
- ecoTEC Plus 620
- ecoTEC Plus 625
- ecoTEC Plus 630
- ecoTEC Plus 635
- ecoTEC Plus 840
- ecoTEC plus aquaPLUS Repair: £80-200
- ecoTEC Pro / ecoTEC Plus
- ecoTEC sustain
- Home Combi
- Home System
- Thermocompact
- Turbomax 824/828 Repair: £120-250
- Turbomax Plus Repair: £120-250
- Turbomax Plus 824/828E
- Turbomax Plus 828
- Turbomax Plus 828 E
- Turbomax Plus VUW 242E
- Turbomax Plus VUW 242EH
Source
Vaillant D.64 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 manual (PDF)
- Vaillant ecoTEC 65kW manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026