BoilerFaultCodesAtag 118 Fault Code
The Atag 118 fault code means: your boiler has detected that the water pressure is too low for it to operate safely, or it is struggling to move water through the system.. It appears on 7 Atag models in our database.
Technical description: Pressure less than 1 bar or pump pressure increase too low (no pump detection).
What causes the Atag 118 fault?
This fault occurs when the boiler's internal sensors detect that the system lacks the minimum water pressure required to circulate heat safely. The most common reason is a slow leak somewhere in the pipework or radiators, but it can also be triggered if the pump has failed and can no longer push water through the heat exchanger.
This code is frequently seen in autumn when the heating is turned on for the first time after summer, as dormant seals may have weeped or air has become trapped in the radiators.
DIY fix possible
Check the pressure gauge on the front of the boiler; it should ideally be between 1.2 and 1.5 bar.Locate the filling loop (usually a silver braided hose with small black lever valves) underneath the boiler.Slowly open the valves to let water in until the gauge reaches 1.5 bar, then ensure they are closed tightly.Press the Reset button on the control panel to clear the fault.
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Gas Safe Register →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 27 April 2026