High Lockout
d3 on Worcester Bosch Greenstar 25HE

Your boiler has lost its connection to an external safety device or a plug-in controller, causing it to stop running as a safety precaution.

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

Jumper 8-9 not detected.

What causes this fault?

This fault occurs when the electrical bridge that completes the safety circuit between the boiler and its external controls is broken. It is usually caused by a loose connection in the wiring, a faulty plug-in wireless receiver, or the small link plug falling out of place. Because the boiler can no longer verify that it is safe to operate, it shuts down immediately to prevent uncontrolled heating.

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 →C6View →

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