BoilerFaultCodesSime ALL 20 Fault Code
Also written as ALL20 — same fault.
The Sime ALL 20 fault code means: your boiler has detected that the water temperature in one of your heating circuits has become dangerously high and has automatically shut itself down to prevent damage.. It appears on 3 Sime models in our database.
Technical description: SAFETY THERMOSTAT INTERVENTION FIRST MIXED ZONE
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 ALL 20 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Sime ALL 20 fault code information on this page is sourced and cross-checked against the official Sime service / installation manuals for each affected model.
- Sime iQE Simplicity 20T manual (PDF)
- Sime Murelle Elite HE 35T System manual (PDF)
- Sime Murelle Elite HE Combi manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026