BoilerFaultCodesSime 03 Fault Code
The Sime 03 fault code means: your boiler has detected that the water pressure inside the heating system is too high, so it has locked out to prevent damage.. It appears on 4 Sime models in our database.
Technical description: High water pressure in system
DIY fix possible
Locate the filling loop valves attached to your boiler or pipework under the unit.Ensure both filling loop valves are fully closed and not letting extra water trickle in.Bleed one or two radiators in your home to release a little water and bring the pressure gauge down to between 1 and 1.5 bar, then reset the boiler.
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Sime models that show the 03 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Sime 03 fault code information on this page is sourced and cross-checked against the official Sime service / installation manuals for each affected model.
- Sime Metropolis DGT 25 BF manual (PDF)
- Sime Murelle Advanced HE MkII Combi manual (PDF)
- Sime Murelle EV HE System manual →
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026