BoilerFaultCodesAtag STOP Fault Code
The Atag STOP fault code means: your boiler is telling you that the internal water pressure is too low, so you need to open your filling loop to top it up to the correct level.. It appears on 6 Atag models in our database.
Technical description: Filling up slowly to 1.5 to 1.7 bar is reached; close filling loop
DIY fix possible
Locate the filling loop, which is usually a silver flexible hose with one or two valves located underneath your boiler.Gradually open the valve(s) to allow water into the system while watching the pressure gauge on the front display.Once the needle reaches 1.5 bar, firmly close the valve(s) and ensure no water is dripping from the connection.
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Gas Safe Register →Atag models that show the STOP fault code
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Source
Atag STOP 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