High Lockout
20 on Glow-worm Xtrafast 120

Your boiler's internal computer parts are struggling to talk to each other, which prevents the system from starting up normally.

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

Communication fault

What causes this fault?

This fault occurs when the boiler's main control board loses the ability to send or receive data from the display panel. The most common reason is a physical connection failure, such as loose wiring or moisture damage to the sensitive circuit boards, which prevents the system from confirming it is safe to fire up.

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

F0View →F1View →

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