G20 Medium

Sime G20 Fault Code

The Sime G20 fault code means: your boiler is displaying a technical configuration code indicating it is calibrating or checking the gas pressure supply to the burner.. It appears on 1 Sime model in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: Gas G20 (Burner Modulator max. pressure mbar)
Typical repair cost £120-250 (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 G20 fault code

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

Source

Sime G20 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