High Lockout
S.3 on Vaillant ecoTEC 65kW

Your boiler is struggling to light its flame, meaning your heating and hot water will likely stop working soon.

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

Heating mode error – ignition problem

What causes this fault?

This fault occurs when the boiler's control system attempts to start the heating cycle but fails to successfully establish or detect a flame. The most common reasons include a worn-out ignition spark, a faulty gas valve not releasing fuel, or the internal sensors becoming too dirty to 'see' the flame once it has lit.

This issue is more frequent during the first cold snap of autumn when internal components that have sat idle all summer are suddenly forced to operate under high demand.

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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