Unit locks out with F2 shortly after ignition, burner shuts down

Safety first: Turn off power and gas. Work only in a well-ventilated area.

Steps:

• Check gas supply: Confirm that the gas cock is fully open and that other gas appliances in the home are working normally. If gas supply is unstable, contact your gas provider.
• Inspect burner: Remove the burner assembly as per Saunier Duval service instructions. Check for dust, rust, or debris blocking the burner ports. Clean with a soft brush and compressed air (low pressure).
• Check ionization electrode: Clean the flame sensing electrode and verify its position relative to the burner flame. Replace if the ceramic is cracked or the rod is heavily corroded.
• Observe operation: With covers reinstalled, restart the unit and watch through the inspection window. If the flame lights but then drops out, the gas valve or PCB modulation control may be faulty and should be checked by a technician with a manometer and combustion analyzer.

Warning: Never adjust internal gas valve settings without proper instruments and authorization. Incorrect adjustment can lead to carbon monoxide production.