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 25 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.
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.65 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £120-£350
- Combi Compact 242EB Repair: £100-£350
- Combi Compact 282EB Repair: £120-350
- ecoFIT pure Repair: £120-350
- ecoFIT Pure 412 Repair: £150-300
- ecoFIT Pure 418 Repair: £100-£280
- ecoFIT Pure 425 Repair: £120-280
- ecoFIT Pure 435 Repair: £120-350
- ecoFIT Pure 835 Repair: £120-350
- ecoTEC Repair: £120-350
- 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 Regular Repair: £120-280
- ecoTEC plus System
- ecoTEC sustain
- Home System Repair: £0-120
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.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026