High Lockout
F.21 on Vaillant ecoMAX Pro 28E

Your boiler has stopped working because it cannot light the flame or keep it burning properly.

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

The pilot flame has failed.

What causes this fault?

This fault occurs when the boiler's control system attempts to light the burner but fails to detect a stable flame after several attempts. The most common reasons are worn-out ignition components that can't create a spark or a faulty sensor that fails to tell the boiler the flame is actually lit.

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.

Find a Gas Safe engineer
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Related fault codes

F.28View →F.29View →

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