BoilerFaultCodesSime AL 03 Fault Code
Also written as AL03 — same fault.
The Sime AL 03 fault code means: your boiler has detected that there is too much water pressure in the system, which can cause the safety valves to trigger or the unit to stop working.. It appears on 12 Sime models in our database.
Technical description: High water pressure in system — drain via hydraulic assembly to ~1.2 bar
DIY fix possible
Locate a radiator bleed valve and use a radiator key to release water into a container until the pressure gauge on the boiler drops to 1.2 bar.Check that the filling loop valves (the silver braided hose beneath the boiler) are fully tightened and not accidentally left open.Restart the boiler to see if the error code clears.
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Sime models that show the AL 03 fault code
Click a model for the full fault code list and model-specific repair notes.
- Brava One HE Repair: £0-120
- Dewy 30/130 HE FS Repair: £0-120
- Dewy 30/50 HE WM Repair: £0-120
- Giulia Combi 30 Repair: £80-220
- Halstead Trio Repair: £80-160
- Mia 30 Repair: £0-120
- Murelle One HE Repair: £0-120
- Murelle Pro HE 25 HO Repair: £0-120
- Murelle Pro HE Combi Repair: £0-120
- Murelle Pro HE MkII Combi Repair: £0-120
- Murelle Pro HE R MkII System Repair: £0-120
- Murelle Pro HE System R Repair: £0-120
Source
Sime AL 03 fault code information on this page is sourced and cross-checked against the official Sime service / installation manuals for each affected model.
- Sime Brava One HE manual (PDF)
- Sime Dewy 30/130 HE FS manual (PDF)
- Sime Dewy 30/50 HE WM manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026