BoilerFaultCodesAtag 118 Fault Code
The Atag 118 fault code means: your boiler has detected that there is not enough water in the system, so it is limiting its performance to protect itself.. 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 filling loop (a flexible metal or plastic pipe) underneath your boiler.Slowly open the valves on the filling loop to allow cold mains water to enter the system.Monitor the pressure gauge on the front of the boiler until the needle reaches the green zone (usually between 1.0 and 1.5 bar).Once the pressure is correct, ensure the filling loop valves are turned firmly off.
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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 7 July 2026