BoilerFaultCodesVaillant D.44 Fault Code
Also written as D44 — same fault.
The Vaillant D.44 fault code means: your boiler's electronic system is struggling to correctly detect the flame signal, which could lead to it locking out for safety.. It appears on 13 Vaillant models in our database.
Technical description: Digitised ionisation – potential error
What causes the Vaillant D.44 fault?
This fault occurs when the boiler's internal computer receives an unstable or unexpected signal from the flame sensing components. It usually happens because the sensor that monitors the flame is dirty, worn out, or the electrical connection between the sensor and the main control board has become weak.
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.44 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £120-300
- ecoMAX Repair: £120-250
- ecoMAX 613 Repair: £150-250
- ecoMAX 618 Repair: £150-300
- ecoMAX 622 Repair: £120-250
- ecoMAX 635 Repair: £150-300
- ecoMAX 824E Repair: £150-300
- ecoMAX 828E Repair: £120-250
- Ecomax Condensing 600/800 series Repair: £120-250
- ecoMAX System 612 Repair: £150-250
- ecoTEC Repair: £120-280
- ecoTEC 65kW Repair: £150-300
- ecoTEC Pro / ecoTEC Plus Repair: £150-300
Source
Vaillant D.44 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
- Vaillant ecoMAX manual (PDF)
- Vaillant ecoMAX System 612 manual (PDF)
- Vaillant ecoMAX 824E manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026