F.538 Medium

Viessmann F.538 Fault Code

Also written as F538 — same fault.

The Viessmann F.538 fault code means: your boiler has lost communication with the temperature sensor that tracks the return flow from your solar thermal heating system, meaning it can no longer accurately monitor heat coming from your solar panels.. It appears on 2 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: No solar central heating backup with SDIO. Lead break, temperature sensor in system return.
Typical repair cost £150-250 (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.538 fault code

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

Source

Viessmann F.538 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