High Lockout
C0 on Keston S30

Your boiler's internal memory chip is not communicating correctly with the main control board, preventing the system from starting up.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

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

Technical description

Boiler Chip Card (BCC) activation fault

What causes this fault?

This fault occurs when the boiler's main control board cannot read the data from the small memory chip that tells it exactly how to operate. This is usually caused by a loose connection where the chip is plugged in, or a physical failure of the chip’s internal circuitry after years of heat exposure.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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