High Lockout
400 on Ideal Response SE

Your boiler's internal computer has encountered a critical electronic error and can no longer control the heating or hot water 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

Internal failure - electronic

What causes this fault?

This fault occurs when the boiler's main control board suffers a hardware failure and can no longer process signals or safety checks. It is often caused by electrical surges, moisture ingress from a small leak, or simple component wear and tear over time. Because the 'brain' of the boiler is damaged, it shuts down instantly to prevent unpredictable behavior.

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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