Unit attempts to ignite but fails, F2 ignition fault displayed

Safety: Switch off power and close the gas valve before working on the heater. Ventilate the area if you smell gas and do not attempt to ignite.

• Visual check of ignition electrode: Remove the burner access cover. Inspect the ignition electrode for cracks in the ceramic, heavy carbon buildup, or a bent tip. Clean light deposits with fine abrasive pad; replace if cracked or heavily eroded.
• Check electrode gap and position: Refer to the Viessmann service manual for the correct spark gap and distance to burner surface. Adjust the electrode bracket so the spark occurs directly over the burner ports.
• Inspect ignition cable: Follow the high-voltage cable from the electrode to the control board. Look for burn marks, cuts, or loose connections. Reseat the cable firmly on both ends.
• Confirm gas supply: Open the external gas shutoff fully. Ensure other gas appliances in the home operate normally. If gas supply is questionable, contact your gas supplier or a licensed gas technician.
• Test ignition: Restore power and gas, then call for hot water. Observe through the sight glass: you should see a strong blue spark. If no spark is visible and wiring/electrode are good, the ignition transformer section of the main PCB may be faulty and requires professional replacement.