High
230V AC on Glow-worm 23c

Your boiler is detecting an electrical fault within its internal control wiring, which means it cannot safely operate and has shut down to protect itself.

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

Between terminals H8.1 and H8.2

From this model's manual
Verified against the Glow Worm 23c True installation & service manual, page 26.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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

F.22View →F.25View →

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