Saunier Duval F28 Error: Gas Ignition Failure
Troubleshoot Saunier Duval F28 error code (ignition & flame sensing failure).
Burner ignition failure or loss of flame ionization signal during startup. The boiler enters safety lockout to prevent unburned gas accumulation.
Probable Causes
Gas supply interruption (closed gas service valve, tripped emergency gas regulator).
Contaminated, oxidized, or defective flame sensing (ionization) electrode.
Faulty gas control valve stepper motor or printed circuit board (PCB) ignition circuit failure.
Diagnostic & Testing Steps
- •Boiler makes 3 audible ignition attempts with spark clicking before failing to establish flame.
- •Flashing F28 code on the digital display accompanied by a red lockout LED.
- •Immediate loss of domestic hot water and central heating circulation.
Tools & Equipment Required
- ✓Torx T20 & Phillips #2 ScrewdriversRemove boiler front casing and sealed combustion chamber access cover.
- ✓Fine Brass Wire Brush / Abrasive PadSafely clean oxidized carbon coating from ionization and ignition electrodes.
- ✓Feeler Gauge (3-4 mm)Verify precise spark gap between ignition pin and burner surface.
- ✓Inspection FlashlightInspect ceramic insulation sleeves for hairline fractures or carbon tracking.
Fast Reset Sequence: Boiler Electronic Flame Lockout Reset
Before unmounting panels or beginning diagnostic procedures, attempt this manufacturer reset to clear transient microcomputer lockouts:
- 1.Locate the flame reset button (marked with 'R' or a flame icon with a cross line).
- 2.Press and hold the button for 3 to 5 seconds until the display flashes or burner light restarts.
- 3.Inspect boiler pressure gauge — water pressure must read between 1.0 and 1.5 bar for safe burner ignition.
- 1
Step 1: Check Gas Inlet Cock & Confirm Supply
[ ] DoneEnsure the gas valve beneath the boiler is fully open and confirm that other gas appliances in the home are receiving normal pressure.
Verification:Gas is present at the meter and no upstream shutoffs are engaged. - 2
Step 2: Clean Ionization Electrode Assembly
[ ] DoneRemove combustion access panel, locate electrode probes near the burner, and polish carbon buildup with fine emery cloth.
Verification:Electrodes are clean, free of black oxide, and gapped to 3-4 mm. - 3
Step 3: Measure Ionization Flame Current & Reset Boiler
[ ] DoneCheck terminal connections on the gas valve assembly, secure the combustion chamber, and press the Reset button.
Verification:Hold Reset for 5 seconds: F28 clears and steady flame establishes.
Repair Solutions
Verify gas supply: check yellow shutoff valve and reset emergency gas regulator if needed.
Clean ignition and flame sensing electrodes with fine emery paper.
Test gas valve solenoid coils and press Reset for 5 seconds to clear lockout.
Frequently Asked Questions
Do I need to replace the main PCB for an F28 error?
No, in over 90% of cases, F28 is caused by gas supply interruptions or dirty ionization probes. The PCB is rarely the root cause.
Can Phase/Neutral electrical reversal trigger F28?
Yes, ionization flame detection requires correct polarity with Neutral-to-Ground voltage strictly below 5 VAC.