BoilerFaultCodesVaillant D.64 Fault Code
Also written as D64 — same fault.
The Vaillant D.64 fault code means: your boiler is taking longer than expected to light the flame, which is currently an advisory warning about its operation.. It appears on 27 Vaillant models in our database.
Technical description: Average ignition times
What causes the Vaillant D.64 fault?
This fault occurs when the boiler's internal computer notices that the burner is taking consistently longer than usual to establish a stable flame. The most common reasons are that the sensors used to detect the flame are becoming dirty or worn, or the gas valve is struggling to provide the correct amount of fuel during the starting sequence.
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.64 fault code
Click a model for the full fault code list and model-specific repair notes.
- aquaPLUS Repair: £80-200
- Atmomax Repair: £90-250
- Combi Compact 242EB Repair: £90-250
- Combi Compact 282EB Repair: £90-250
- ecoFIT pure Repair: £120-350
- ecoFIT Pure 412 Repair: £120-250
- ecoFIT Pure 418 Repair: £100-250
- ecoFIT Pure 425 Repair: £80-200
- ecoFIT Pure 435 Repair: £100-250
- ecoFIT Pure 835 Repair: £100-250
- ecoTEC Repair: £100-250
- 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 Regular Repair: £100-250
- ecoTEC plus System
- ecoTEC sustain
- Home System
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.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026