How much does it cost to fix Viessmann error code 6C:0 to 6C:100?

Typical repair cost for the Viessmann 6C:0 to 6C:100 fault is £150-450 including labour.

6C:0 to 6C:100 Medium

Viessmann 6C:0 to 6C:100 Fault Code

Q: What does the Viessmann 6C:0 to 6C:100 fault code mean?

Your boiler's internal pump or fan is reporting an incorrect speed setting, which is usually a technical communication error between the internal computer and the parts that move water or air.

Also written as 6C0TO6C100 — same fault.

The Viessmann 6C:0 to 6C:100 fault code means: your boiler's internal pump or fan is reporting an incorrect speed setting, which is usually a technical communication error between the internal computer and the parts that move water or air.. It appears on 5 Viessmann models in our database.

Technical description: Set speed adjustable from 0 to 100%

What causes the Viessmann 6C:0 to 6C:100 fault?

This fault occurs when the boiler's control board sends a command to the pump or fan but receives a confused or incorrect speed signal in return. It is essentially a communication breakdown where the internal computer cannot confirm that these vital moving parts are spinning at the correct rate to safely manage heat and airflow.

Typical repair cost £150-450 (including labour)

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 6C:0 to 6C:100 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Viessmann 6C:0 to 6C:100 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