BoilerFaultCodesAtag 81 Fault Code
The Atag 81 fault code means: your boiler has detected that a critical safety sensor responsible for monitoring exhaust gases has become disconnected, so it has safely shut itself down to prevent operation until the issue is fixed.. It appears on 6 Atag models in our database.
Technical description: The flue gas sensor is not connected although it has been connected to the control. The burner is blocked until the flue gas sensor is reconnected.
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 81 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Atag 81 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 7 July 2026