High Lockout
F1 on Glow-worm Ultimate

Your boiler has lost power to its internal electronics, likely caused by a safety fuse blowing or an electrical fault inside the unit.

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

Fuse Type (F1A)

What causes this fault?

This fault occurs when the boiler's internal electrical protection system detects an overload or a short circuit, causing a safety fuse to blow. The most common reason is an electrical component, such as the pump or a valve, failing and drawing too much current, which cuts power to the control board to prevent further damage.

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

F2View →

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