High
F4 on Saunier Duval Isotwin F30E

Your boiler is unable to safely light the flame needed 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.

What the manual says

Manufacturer manual

Ignition fault, boiler failed to light

Shared across the range
This code is shared by the boilers in this range, which use the same control board. It may not be printed in this exact variant’s manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this fault?

This fault occurs when the boiler attempts to ignite several times but fails to establish or detect a steady flame. It is often caused by a lack of gas reaching the burner, worn-out spark electrodes, or a faulty sensor that cannot confirm the flame is safely lit.

This fault is more common during extreme cold snaps, as freezing temperatures can cause external gas regulators to stick or thin pipes to become restricted.

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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