High Lockout
D.93 on Vaillant ecoTEC plus Regular

Your boiler’s computer is confused about which specific model it is supposed to be, usually happening after a major part has been replaced.

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

DSN appliance variant setting

What causes this fault?

This fault occurs when the boiler's main control board has lost its identity and doesn't know which power output or model size it is controlling. It most frequently happens after a new circuit board has been installed but hasn't been programmed with the correct device specific number. Without this data, the boiler stays in a safety mode because it doesn't know how much gas to burn or how fast to run the internal components.

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.70View →

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