Boiler does not start; display shows A2 and burner symbol does not appear

Safety first: Turn the boiler off at the main switch and isolate the gas supply before removing any covers. Only a Gas Safe / certified gas technician should work on gas-carrying components.

• Check gas supply: Ensure the gas cock under the Junkers boiler is fully open. Verify other gas appliances in the home work correctly. If not, contact your gas supplier.
• Reset the boiler: Use the reset button (often marked with a flame or reset symbol) and wait for a full ignition cycle. If A2 reappears, continue.
• Inspect flue terminal: From outside, make sure the flue is not blocked by leaves, snow, or debris, which can affect combustion.
• Check flame viewing window: If accessible without removing the sealed combustion cover, observe whether the burner lights briefly and then goes out. This indicates poor flame detection.
• Professional checks (technician only):
  • Remove front cover and inspect the ionisation electrode for cracks, heavy oxidation, or incorrect gap; clean lightly with fine emery cloth and refit or replace.
  • Measure ionisation current according to Junkers service manual; if low, replace the ionisation electrode and check burner surface for contamination.
  • Verify correct gas pressure at the inlet and at the burner using a manometer; adjust or replace the gas valve if out of specification.
  • Check wiring harness between electrode and control board for damage or loose connections.