High Lockout
F4 on Vaillant ecoMAX Pro 28E

Your boiler has failed to keep the flame lit and has locked itself out 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

Ignition fault (lockout) Went out when lit

What causes this fault?

This fault occurs when the boiler successfully lights but then immediately loses the flame signal, causing it to shut down for safety. The most common reasons are worn-out sensors that can no longer 'see' the flame or a gas valve that isn't providing a steady enough flow of fuel to keep the burner 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.

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