BoilerFaultCodesAtag 109 Fault Code
The Atag 109 fault code means: your boiler has too much water pressure inside the system, which has triggered a safety shutdown to protect the internal components.. It appears on 2 Atag models in our database.
Technical description: Pressure >Pmax
DIY fix possible
Check that the internal or external filling loop valves are tightly closed.Bleed water from a radiator using a radiator key to lower the pressure on the boiler's gauge.Ensure the pressure returns to the green zone (usually 1.0 to 1.5 bar) and restart the boiler.
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Atag models that show the 109 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Atag 109 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