BoilerFaultCodesVaillant D.44 Fault Code
Also written as D44 — same fault.
The Vaillant D.44 fault code means: your boiler is having trouble managing its flame correctly and has shut down as a safety precaution.. It appears on 6 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 is unable to correctly measure or verify the electrical signal sent back by the flame. It usually happens because the sensing electrode has become worn or carbon-coated, or because the gas valve is not delivering the precise mixture needed to sustain a steady burner signal. Without this confirmation that the flame is safe and stable, the boiler enters a safety shutdown.
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.44 fault code
Click a model for the full fault code list and model-specific repair notes.
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.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026