High Lockout
F7 on Worcester Bosch Greenstar 12i System

Your boiler thinks it can still see a flame inside even though it has been told to turn off, which is a safety conflict that prevents it from starting up again.

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

Flame detected even though appliance is switched off

What causes this fault?

This fault occurs when the boiler's control system detects an electrical signal from the flame sensor at a time when the gas should be completely shut off. The most common reason is a contaminated or damaged sensor sending a false signal, or a gas valve that is failing to close fully and allowing a tiny amount of fuel to continue burning.

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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Related fault codes

C1View →EAView →FDView →

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