BoilerFaultCodesSime AL 01 Fault Code
Also written as AL01 — same fault.
The Sime AL 01 fault code means: your boiler has detected that dangerous exhaust gases are not being cleared safely through the chimney, causing it to shut down to prevent carbon monoxide from entering your home.. It appears on 13 Sime models in our database.
Technical description: Smoke thermostat (flue gas thermostat) intervention — open-flue variants only
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A cover plan would handle faults like AL 01: no call-out fees, no surprise bills.
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Sime models that show the AL 01 fault code
Click a model for the full fault code list and model-specific repair notes.
- Brava One HE Repair: £100-220
- Dewy 30/130 HE FS Repair: £100-£250
- Dewy 30/50 HE WM Repair: £120-250
- Ecomfort Plus HE EV Combi Repair: £150-300
- Ecomfort System Plus HE EV Repair: £100-250
- Halstead Trio Repair: £120-250
- Mia 30 Repair: £150-300
- Murelle One HE Repair: £120-250
- Murelle Pro HE 25 HO Repair: £120-280
- Murelle Pro HE Combi Repair: £120-250
- Murelle Pro HE MkII Combi Repair: £120-250
- Murelle Pro HE R MkII System Repair: £120-250
- Murelle Pro HE System R Repair: £120-250
Source
Sime AL 01 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