High Lockout
S.23 on Vaillant ecoTEC exclusive

Your boiler is currently struggling to light the flame it needs to provide heating and hot water.

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

DHW mode: Ignition

What causes this fault?

This fault occurs when the boiler is unable to successfully establish a flame after several attempts. The most common reasons are a lack of gas supply to the unit, a worn-out ignition electrode that is failing to create a spark, or a faulty gas valve that isn't opening correctly.

This issue can occur in winter if the external gas regulator freezes or if the gas meter becomes restricted by extreme cold.

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
Search the official register →

Related fault codes

Related guides you might find useful