BoilerFaultCodes.com
C6 High Lockout

Your boiler's fan is spinning faster than it should, which means the system has safely shut down to prevent any damage.

Call an engineer soon

Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Fan speed too high.

What causes this fault?

This fault occurs when the boiler's control system detects that the fan is spinning at an uncontrolled or excessive speed, which prevents the correct mix of air and gas for safe combustion. It is typically caused by a communication failure between the main circuit board and the fan, or a mechanical defect within the fan motor itself. Because the boiler cannot accurately regulate the flame with the fan running too fast, it shuts down as a safety precaution.

Typical repair cost £200-£450 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Protect yourself from future repair bills

A boiler cover plan would cover faults like C6 — no call-out fees, no surprises.

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