High
Neon 1 lit on Glow-worm Ultimate

Your boiler has detected an electrical supply issue, likely caused by a tripped switch, a blown fuse, or a temporary power failure.

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.

What the manual says

Manufacturer manual

Fault with mains supply or PCB fuse

From this model's manual
Verified against the Glow Worm Ultimate System installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this fault?

This fault occurs when the boiler's control system detects an interruption or an irregularity in the electrical current reaching the unit. It is most commonly caused by a blown 3-amp fuse in the external spur switch or a failure within the boiler's internal circuit board which prevents it from processing power correctly.

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

Neon 2View →Neon 3View →

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