High Lockout
F0 on Worcester Bosch 537i

Your boiler's computer system has encountered an internal technical glitch that is preventing it from operating correctly.

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

Internal error.

What causes this fault?

This fault occurs when the boiler's main control board suffers a critical electronic failure, essentially losing its ability to process data or talk to the sensors. The most common reason is an electrical surge or a component failure within the circuit board's internal memory. Because the 'brain' of the boiler can no longer guarantee safe operation, it shuts the system down entirely.

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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