High
F4 on Saunier Duval Themaclassic F24E

Your boiler is attempting to start its flame but is unable to stay lit, causing it to shut down for safety reasons.

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.

What the manual says

Manufacturer manual

Ignition fault / The burner lights, then goes out. Flame not being detected via the flame sense electrode and terminal H2.4 on the control board.

From this model's manual
Verified against the Saunier Duval Themaclassic F24e installation & service manual, page 37.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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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