ALL 33 High

Sime ALL 33 Fault Code

Also written as ALL33 — same fault.

The Sime ALL 33 fault code means: your boiler's internal electronic parts are having trouble talking to each other, which has caused the system to stop working as a safety precaution.. It appears on 1 Sime model in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: rs-485 Board communication Er- ror in modBus modE
Typical repair cost £150-300 (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 33 fault code

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

Source

Sime ALL 33 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