How much does it cost to fix Sime error code ALL 12?

Typical repair cost for the Sime ALL 12 fault is £120-200 including labour.

ALL 12 High

Sime ALL 12 Fault Code

Q: What does the Sime ALL 12 fault code mean?

Your boiler has lost its correct settings for how it handles air intake and exhaust, which means it has safely stopped working to prevent incorrect operation.

Also written as ALL12 — same fault.

The Sime ALL 12 fault code means: your boiler has lost its correct settings for how it handles air intake and exhaust, which means it has safely stopped working to prevent incorrect operation.. It appears on 3 Sime models in our database.

Technical description: Incorrect configuration of the open /sealed chamber

Typical repair cost £120-200 (including labour)

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 12 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Sime ALL 12 fault code information on this page is sourced and cross-checked against the official Sime service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026