125 High

Sime 125 Fault Code

The Sime 125 fault code means: your boiler has detected that the water is heating up far too quickly or that the flow of water is insufficient, causing the system to shut down to prevent damage.. 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: 4.6=h recapS
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 125 fault code

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

Source

Sime 125 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