How much does it cost to fix Main error code 109?

Typical repair cost for the Main 109 fault is £150-300 including labour.

109 High

Main 109 Fault Code

Q: What does the Main 109 fault code mean?

Your boiler has detected an internal system error that is preventing it from operating safely, causing it to shut down to protect itself.

The Main 109 fault code means: your boiler has detected an internal system error that is preventing it from operating safely, causing it to shut down to protect itself.. It appears on 1 Main model in our database.

Technical description: Fault detected

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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Main models that show the 109 fault code

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

Insul 7 Repair: £150-300

Source

Main 109 fault code information on this page is sourced and cross-checked against the official Main service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026