High Lockout
T.03 on Vaillant ecoTEC Plus 620

Your boiler's fan is struggling to start or run at the correct speed, which is preventing the boiler from firing up for safety.

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

Fan

What causes this fault?

This fault occurs when the boiler's control system detects that the fan is not spinning at the required speed to safely clear exhaust gases. The most common reasons are a mechanical failure within the fan motor itself or a communication issue where the main circuit board is unable to send power or instructions to the fan.

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.32View →F.33View →

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