BoilerFaultCodesAtag 04 Fault Code
The Atag 04 fault code means: your boiler has experienced a power interruption or an electrical stability issue, causing it to temporarily lose its settings or shutdown.. It appears on 6 Atag models in our database.
Technical description: adjustment or error for voltage interruption
DIY fix possible
Locate the boiler's fused spur switch or the dedicated circuit breaker in your fuse box.Switch the power off for 30 seconds to allow the internal electronics to reset.Switch the power back on and check if the boiler restarts and the error clears.
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Atag models that show the 04 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Atag 04 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