High Lockout
F0 on Worcester Bosch Greenstar CDi Compact

Your boiler's internal computer has encountered a critical electronic glitch that is preventing it from running safely.

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

Internal error / Sensor test failed / Recycle time error / Too many short burner starts without confirmation

What causes this fault?

This fault occurs when the boiler's central control board suffers a critical electronic failure, meaning it can no longer communicate with the internal components. The most common reason is a hardware malfunction within the circuitry or an electrical surge that has damaged the delicate microprocessors. In some cases, loose or damaged wiring connections between the board and the sensors can also trigger this shutdown.

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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