C6:75 Medium

Viessmann C6:75 Fault Code

Also written as C675 — same fault.

The Viessmann C6:75 fault code means: your boiler has detected that the water inside is getting too hot and has temporarily restricted itself to prevent overheating and ensure safe operation.. It appears on 6 Viessmann models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: Electronic maximum flow temperature limit at 75°C
Typical repair cost £150-300 (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 C6:75 fault code

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

Source

Viessmann C6:75 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