BoilerFaultCodesSaunier Duval F4 Fault Code
The Saunier Duval F4 fault code means: your boiler is unable to safely light the flame needed to provide heating and hot water.. It appears on 9 Saunier Duval models in our database.
Technical description: Ignition fault, boiler failed to light
What causes the Saunier Duval F4 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.
DIY fix possible
Check that your gas prepayment meter has credit (if applicable)Verify that other gas appliances, such as a hob, are working correctlyPress and hold the reset button (flame symbol with a cross) for five seconds
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Search the official register for a qualified engineer in your area.
Gas Safe Register →Saunier Duval models that show the F4 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Saunier Duval F4 fault code information on this page is sourced and cross-checked against the official Saunier Duval service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026