F.64 Medium

Viessmann F.64 Fault Code

Also written as F64 — same fault.

The Viessmann F.64 fault code means: your boiler is struggling to keep the flame lit while it is starting up, so it is automatically turning itself off and trying again to get back to normal.. It appears on 1 Viessmann model 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: Normal operation Flame loss during stabilisation or operating phase. Burner restarts.
Typical repair cost £150-350 (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 F.64 fault code

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

Source

Viessmann F.64 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