BoilerFaultCodesSime ALL03 Fault Code
The Sime ALL03 fault code means: your boiler has too much water inside it, causing the internal pressure to rise to an unsafe level.. It appears on 1 Sime model in our database.
Technical description: The system pressure detected is more than 2.8 bar. Ensure that the filling loop is turned off and the pipe detatched. Lower the system pressure by draining from a radiator, if problem persists seek help from a qualified engineer.
DIY fix possible
Check that the silver filling loop taps underneath the boiler are tightly closed.Locate a radiator bleed valve and use a key to slowly release water into a container.Monitor the boiler pressure gauge until it drops back down to between 1.0 and 1.5 bar.
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Sime models that show the ALL03 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Sime ALL03 fault code information on this page is sourced and cross-checked against the official Sime service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026