dA Low

Viessmann dA Fault Code

Also written as DA — same fault.

The Viessmann dA fault code means: your boiler has lost its connection to the indoor thermostat sensor, meaning it can no longer adjust the heating based on the actual temperature inside your home.. It appears on 7 Viessmann models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Control mode without room influence - Room temperature sensor heating circuit A1 shorted out

What causes the Viessmann dA fault?

This fault occurs when the communication link between your boiler and the indoor temperature sensor is broken. The most common cause is a physical failure of the sensor’s internal components or a loose connection in the wiring that tethers the sensor to the boiler’s main control board.

Typical repair cost £90-180 (including labour)

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 →

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 27 April 2026