How much does it cost to fix Viessmann error code C5:20?

Typical repair cost for the Viessmann C5:20 fault is £120-250 including labour.

C5:20 Medium

Viessmann C5:20 Fault Code

Q: What does the Viessmann C5:20 fault code mean?

Your boiler has detected that the water temperature is currently below the required minimum safety level, causing it to pause heating to prevent potential condensation issues.

Also written as C520 — same fault.

The Viessmann C5:20 fault code means: your boiler has detected that the water temperature is currently below the required minimum safety level, causing it to pause heating to prevent potential condensation issues.. It appears on 6 Viessmann models in our database.

Technical description: Electronic minimum flow temperature limit 20°C

Typical repair cost £120-250 (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 C5:20 fault code

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

Source

Viessmann C5:20 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