How much does it cost to fix Atag error code C 78?

Typical repair cost for the Atag C 78 fault is £150-350 including labour.

C 78 High

Atag C 78 Fault Code

Q: What does the Atag C 78 fault code mean?

Your boiler has detected that there is either too little water circulating through the system or that the internal pump responsible for moving that water has stopped working.

Also written as C78 — same fault.

The Atag C 78 fault code means: your boiler has detected that there is either too little water circulating through the system or that the internal pump responsible for moving that water has stopped working.. It appears on 4 Atag models in our database.

Technical description: Water pressure not connected or pump failure

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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Atag models that show the C 78 fault code

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

Source

Atag C 78 fault code information on this page is sourced and cross-checked against the official Atag service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026