How much does it cost to fix Main error code 5 flashes red?

Typical repair cost for the Main 5 flashes red fault is £150-300 including labour.

5 flashes red High

Main 5 flashes red Fault Code

Q: What does the Main 5 flashes red fault code mean?

Your boiler's internal computer is experiencing a communication error, meaning it has forgotten its operating settings and cannot safely start up.

Also written as 5FLASHESRED — same fault.

The Main 5 flashes red fault code means: your boiler's internal computer is experiencing a communication error, meaning it has forgotten its operating settings and cannot safely start up.. It appears on 1 Main model in our database.

Technical description: Parameter fault (Bad connection to PU, Parameter error or faulty PU)

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 5 flashes red fault code

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

Insul 7 Repair: £150-300

Source

Main 5 flashes red 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