Boiler attempts to ignite but fails; you may hear clicking but no flame, then the boiler locks out with EA.

Safety: If you smell gas, do not attempt to reset the boiler. Turn off the gas at the meter, ventilate the area, and call the gas emergency number and a Gas Safe engineer immediately.

User checks:

• Confirm that the gas isolation valve to the boiler is open.
• Check if other gas appliances (hob, fire) work. If none work, there may be a supply issue.
• Reset the boiler following the Bosch user instructions. Observe whether the boiler tries to ignite (fan runs, clicking heard).

Technician checks (for reference):

• Inspect and clean the ignition and ionisation electrodes; check gap and condition.
• Check gas valve operation and inlet pressure.
• Verify correct polarity and earth on the electrical supply, as flame sensing relies on proper earthing.

Do not attempt to dismantle the burner or gas valve yourself. Ignition and combustion faults must be rectified by a qualified gas engineer.