Safety first: Isolate electrical power and close the gas valve. Allow the unit to cool before working near the burner.

Steps:

Visual inspection: Remove the front cover and inspect the ignition electrode on the burner assembly. Check for cracks in the ceramic, heavy soot, or corrosion.
Clean electrode: Gently clean the electrode tip with fine emery cloth. Do not bend the electrode rod. Ensure the electrode is positioned as per Saunier Duval specifications (correct distance to burner surface).
Check ignition cable: Inspect the high-voltage cable from the PCB to the electrode for cuts, burns, or loose connections. Reseat both ends firmly.
Check earth/ground: Ensure the appliance is properly earthed; poor grounding can prevent flame detection.
Test restart: Restore gas and power, then reset the heater and observe ignition. If F1 returns, the PCB ignition/flame circuit may be defective and should be tested and replaced by a qualified technician.

Warning: Do not operate the heater with the combustion chamber open. Risk of flue gas spillage and fire.

Water heater attempts to start but shuts down with F1, no flame established

Possible Causes