High Lockout
F66 on Ferroli Modena HE

Your boiler's main internal computer has developed a technical fault and can no longer control the heating system safely.

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

Controller ABM03B error – controller internal error

What causes this fault?

This fault occurs when the boiler's internal computer chips suffer a hardware failure or a memory corruption, meaning the board can no longer process safety data correctly. The most common reason is electrical degradation of the circuitry over time or a sudden power surge that damages the sensitive components on the PCB.

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

A61View →

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