BoilerFaultCodesSime AL 42 Fault Code
Also written as AL42 — same fault.
The Sime AL 42 fault code means: your boiler has detected that one of its control buttons is stuck or faulty, which is preventing you from changing settings or operating the unit properly.. It appears on 14 Sime models in our database.
Technical description: Button fault — verify all control buttons function; check PCB
DIY fix possible
Carefully press and release each button on the control panel to see if any are physically stuck or jammed.Gently wipe the control panel with a dry, lint-free cloth to ensure no debris is interfering with the buttons.Turn the power supply to the boiler off and back on again to reset the electronic controls.
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Sime models that show the AL 42 fault code
Click a model for the full fault code list and model-specific repair notes.
- Brava One HE Repair: £120-300
- Brava Slim HE Regular Repair: £100-£280
- Brava Slim HE System Repair: £100-£350
- Dewy 30/130 HE FS Repair: £120-350
- Dewy 30/50 HE WM Repair: £120-350
- Giulia Combi 30 Repair: £90-250
- Halstead Trio Repair: £180-350
- Mia 30 Repair: £100-250
- Murelle One HE Repair: £120-300
- Murelle Pro HE 25 HO Repair: £120-350
- Murelle Pro HE Combi Repair: £100-£350
- Murelle Pro HE MkII Combi Repair: £100-280
- Murelle Pro HE R MkII System Repair: £120-280
- Murelle Pro HE System R Repair: £120-£280
Source
Sime AL 42 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