BoilerFaultCodesVaillant D.65 Fault Code
Also written as D65 — same fault.
The Vaillant D.65 fault code means: your boiler is struggling to spark or light the gas correctly, which is a safety mechanism preventing it from trying to ignite for too long.. It appears on 28 Vaillant models in our database.
Technical description: Maximum ignition time
What causes the Vaillant D.65 fault?
This fault occurs when the boiler's internal safety system detects that the gas has failed to ignite within the safe time limit allowed. The most common reasons are that the spark electrode is too worn to create a flame, or the gas valve isn't opening correctly to let fuel into the burner. In some cases, it can also be caused by a blockage in the flue or a fault in the main control board failing to send the ignition signal.
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.65 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £120-£350
- ecoFIT Pure 418 Repair: £100-£280
- ecoFIT Pure 425 Repair: £120-280
- ecoFIT Pure 435 Repair: £120-350
- ecoFIT Pure 825 Repair: £150-350
- ecoFIT Pure 830 Repair: £150-350
- ecoFIT Pure 835 Repair: £120-350
- ecoTEC Repair: £120-350
- ecoTEC 65kW Repair: £180-350
- ecoTEC Plus 615
- ecoTEC Plus 620
- ecoTEC Plus 625
- ecoTEC Plus 630
- ecoTEC Plus 635
- ecoTEC Plus 840
- ecoTEC plus aquaPLUS Repair: £120-250
- ecoTEC Pro / ecoTEC Plus Repair: £150-300
- ecoTEC sustain
- Home Combi Repair: £150-350
- Home System Repair: £0-120
- Thermocompact Repair: £150-300
- Turbomax 824/828 Repair: £150-250
- Turbomax Plus Repair: £150-300
- Turbomax Plus 824/828E Repair: £150-300
- Turbomax Plus 828 Repair: £150-300
- Turbomax Plus 828 E Repair: £150-300
- Turbomax Plus VUW 242E Repair: £150-300
- Turbomax Plus VUW 242EH Repair: £120-250
Source
Vaillant D.65 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