How much does it cost to fix Main error code 4 flashes green?

Typical repair cost for the Main 4 flashes green fault is £120-250 including labour.

4 flashes green High

Main 4 flashes green Fault Code

Q: What does the Main 4 flashes green fault code mean?

Your boiler's internal computer is struggling to talk to its internal parts, meaning it has paused operations as a safety precaution until the signal issue is resolved.

Also written as 4FLASHESGREEN — same fault.

The Main 4 flashes green fault code means: your boiler's internal computer is struggling to talk to its internal parts, meaning it has paused operations as a safety precaution until the signal issue is resolved.. It appears on 1 Main model in our database.

Technical description: Communication fault: Bad connection or wiring fault, Internal communication fault

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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Main models that show the 4 flashes green fault code

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

Insul 7 Repair: £120-250

Source

Main 4 flashes green 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