High Lockout
E4 on Baxi Duo-tec Combi

Your boiler is not firing up properly, which means it cannot light the gas to provide heat or hot water.

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 failure

What causes this fault?

This fault occurs when the boiler tries to light the gas but fails to detect a flame after several attempts. The most common reasons include a worn-out ignition spark, a faulty gas valve that isn't letting fuel through, or an issue with the electrical circuit board that controls the starting sequence.

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

E128View →E133View →

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