Viessmann A6 Fault

Viessmann A6 Fault

The Viessmann A6 fault code pertains to a communication error between the boiler’s control unit and the burner’s control unit. This fault indicates that the two units are unable to communicate effectively, which can impact the boiler’s operation, including its ability to ignite and function properly. Here’s a closer look at the potential causes and steps to address the A6 fault code:

Causes of the A6 Fault Code

  1. Wiring Issues: Faulty or loose wiring connections between the boiler’s control unit and the burner’s control unit can disrupt communication, leading to the A6 error.
  2. Faulty Control Units: Either the boiler’s main control unit or the burner’s control unit may be malfunctioning, which can prevent effective communication between the two.
  3. Software or Configuration Errors: Errors in the software or configuration settings within the control units can also cause communication problems, resulting in the A6 fault code.
  4. Power Supply Problems: Interruptions or inconsistencies in the power supply to the boiler or control units can impact their ability to communicate.

Troubleshooting and Resolving the A6 Fault Code

  1. Check Wiring Connections: Inspect the wiring connections between the boiler’s control unit and the burner’s control unit for any signs of damage, wear, or looseness. Secure any loose connections and replace damaged wires if necessary.
  2. Reset the Boiler: Attempt to reset the boiler to see if the communication error clears. This can sometimes resolve temporary glitches or software issues.
  3. Inspect Control Units: Check both the boiler’s and burner’s control units for any visible signs of damage or malfunction. This step should be performed by a qualified technician due to the complexity of the units.
  4. Consult the Manual: Refer to your boiler’s manual for any specific instructions or troubleshooting steps related to the A6 fault code. The manual may provide additional insights into resolving communication errors.
  5. Professional Diagnosis and Repair: Due to the technical nature of communication errors and the potential need for software diagnostics or configuration adjustments, it’s advisable to contact a Viessmann-certified technician or a Gas Safe registered engineer for professional diagnosis and repair.
  6. Regular Maintenance: Ensure that your boiler receives regular maintenance by a qualified professional. This can help prevent communication errors and other faults by ensuring that all components, including wiring and control units, are in good working order.


The Viessmann A6 fault code highlights a communication issue between the boiler’s and burner’s control units, which requires careful inspection and potentially complex troubleshooting. Addressing this fault often involves technical knowledge and skills, making it important to seek professional assistance. Regular boiler maintenance can also play a crucial role in preventing such communication errors and ensuring the reliable operation of your heating system.