BoilerFaultCodesSime AL 12 Fault Code
Also written as AL12 — same fault.
The Sime AL 12 fault code means: your boiler's computer has been set to the wrong ventilation mode, causing it to shut down for safety because it thinks it is installed in a different type of building setup.. It appears on 15 Sime models in our database.
Technical description: Incorrect configuration of the open/sealed chamber — set parameter PAR 04 (Combustion configuration) to 0 for sealed chamber
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Sime models that show the AL 12 fault code
Click a model for the full fault code list and model-specific repair notes.
- Brava One HE Repair: £80-130
- Brava Slim HE Regular Repair: £80-130
- Brava Slim HE System Repair: £80-150
- Dewy 30/130 HE FS Repair: £80-160
- Dewy 30/50 HE WM Repair: £80-160
- Giulia Combi 30 Repair: £90-160
- Halstead Trio Repair: £80-130
- Metropolis DGT 25 BF Repair: £80-140
- Mia 30 Repair: £90-160
- Murelle One HE Repair: £80-120
- Murelle Pro HE 25 HO Repair: £120-220
- Murelle Pro HE Combi Repair: £80-120
- Murelle Pro HE MkII Combi Repair: £80-140
- Murelle Pro HE R MkII System Repair: £80-£120
- Murelle Pro HE System R Repair: £80-120
Source
Sime AL 12 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 Brava Slim HE System manual (PDF)
- Sime Dewy 30/130 HE FS manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026