High
Neon 1 lit (No) on Glow-worm Ultimate3 Combi

Your boiler has lost electrical power, which is usually caused by an issue with the mains supply or a blown internal fuse.

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 Ultimate 30ff 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 is not receiving the electrical power it needs to operate, causing the control panel to go dark except for the error light. The most common reason is a blown fuse on the main circuit board or a tripped switch in your home's fuse box, often triggered by a sudden power surge or a failing internal component. In some cases, it can simply be that the external power switch for the boiler has been accidentally turned off.

This fault is slightly more common during the winter months when power grids are under higher load or during stormy weather, as electrical surges and lightning strikes are more likely to blow sensitive internal fuses.

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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