High Lockout
F43 on Glow-worm Flexicom hx

Your boiler's main control unit is confused because a specific internal configuration component is missing or has the wrong electrical profile.

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

Coded resistance fault

What causes this fault?

This fault occurs when the boiler's main control board loses its identity because a small electronic component called a coding chip is loose, damaged, or missing. The chip tells the computer exactly which model of boiler it is controlling, and without this information, the system shuts down for safety. The most common reason is a component failure within the electrical circuit or a loose connection following a recent repair.

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

F70View →

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