How much does it cost to fix Atag error code Error 18?

Typical repair cost for the Atag Error 18 fault is £150-300 including labour.

Error 18 High

Atag Error 18 Fault Code

Q: What does the Atag Error 18 fault code mean?

Your boiler has detected that the water inside the system has become dangerously hot and has shut itself down to prevent damage or overheating.

Also written as ERROR18 — same fault.

The Atag Error 18 fault code means: your boiler has detected that the water inside the system has become dangerously hot and has shut itself down to prevent damage or overheating.. It appears on 5 Atag models in our database.

Technical description: maximum flow temperature exceeded

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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Atag models that show the Error 18 fault code

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

Source

Atag Error 18 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