BoilerFaultCodesViessmann dA Fault Code
Also written as DA — same fault.
The Viessmann dA fault code means: your boiler has lost its connection to the indoor temperature sensor for your main heating area, meaning it cannot accurately tell how warm your rooms are.. It appears on 1 Viessmann model in our database.
Technical description: Short circuit, room temperature sensor, heating circuit 1 (without mixer)
What causes the Viessmann dA fault?
This fault occurs when the electrical signal from your indoor temperature controller is interrupted or becomes inconsistent. The most common reason is a loose connection in the wiring or a failure of the internal sensor component that detects the heat level in your home.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Viessmann models that show the dA fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann dA fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026