BoilerFaultCodesAtag 118 Fault Code
The Atag 118 fault code means: your boiler has lost some water pressure, so it is working less efficiently to prevent internal damage until you add more water to the system.. It appears on 3 Atag models in our database.
Technical description: Water pressure is too low (<1.0 bar). Power is reduced by 20%. The installation should be refilled.
DIY fix possible
Locate the external filling loop, usually a silver braided hose with one or two valves underneath your boiler.Open the valves slowly to allow mains water into the heating system while watching the pressure gauge on the front of the boiler.Stop the flow once the needle reaches the green zone, typically between 1.2 and 1.5 bar, and ensure both valves are firmly closed.
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Atag models that show the 118 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Atag 118 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 31 August 2026