BoilerFaultCodesAtag HIGH Fault Code
The Atag HIGH fault code means: your boiler has stopped working because the water pressure inside the system has become too high, which is a safety mechanism to prevent damage.. It appears on 8 Atag models in our database.
Technical description: Water pressure is to high (>2,8 bar), HIGH indication remains continuously visible, the boiler is taken out of operation. The installation pressure needs to be decreased by draining water.
DIY fix possible
Locate a radiator bleed valve and use a key to release water into a container until the pressure gauge drops to 1.5 bar.Alternatively, use a drain-off valve at a low point in the system to remove excess water.Check that the filling loop valves are fully closed and not passing water into the system.
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Gas Safe Register →Atag models that show the HIGH fault code
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Source
Atag HIGH 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