BoilerFaultCodesAtag 1P4 Fault Code
The Atag 1P4 fault code means: your boiler has detected that the water pressure is getting low and needs to be topped up to keep the system running correctly.. It appears on 2 Atag models in our database.
Technical description: Pressure 0.5–0.8 bar — filling needed
DIY fix possible
Locate the external filling loop, which is usually a silver flexible hose with one or two small taps.Slowly open the tap(s) until you hear water flowing into the system.Watch the pressure gauge on the boiler until it reaches between 1.2 and 1.5 bar, then close the taps tightly.
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Atag models that show the 1P4 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Atag 1P4 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