High Lockout
S13 on Vaillant ecoTEC Pro / ecoTEC Plus

Your boiler is struggling to light properly when you turn on your hot water taps.

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 error

What causes this fault?

This fault occurs when the boiler detects that the burner is failing to light or stay lit specifically while trying to heat your domestic hot water. The most common reasons are a weak spark from worn-out ignition parts or a gas valve that isn't opening correctly to provide fuel. It can also be caused by moisture on the electrodes or a communication error within the core control board.

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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