Error FA 306

Safety first

1) If you smell gas, stop immediately, do not operate electrical switches, open windows, ventilate the area and call the gas emergency number (and a Gas Safe engineer).

2) If the boiler is locked out, do not keep repeatedly resetting it. Repeated lockouts can be dangerous and mask a fault that needs a qualified engineer.

3) Before doing any checks: turn the boiler off at the programmer and isolate electrical supply at the fused spur. If you open the boiler casing, only do so if you are competent and comfortable, but do not work on gas-carrying components unless you are Gas Safe registered.

Initial homeowner checks (safe, simple checks you can do)

1) Note the exact error on the display and the cause code (if shown). Photograph the display for the engineer.

2) Try a single reset: press and hold the boiler reset button for 3 seconds (or follow your manual reset procedure). If the error does not return, monitor but book an engineer if it reappears.

3) Check the boiler and surrounding area for signs of water ingress or condensation around the electrode area or wiring. Moisture can cause spurious ionisation signals.

4) Ensure the flue termination is clear and that the appliance is mounted dry and sheltered; heavy rain or condensation on the flue or burner area can occasionally cause false signals.

5) Visually inspect any exposed ignition/ionisation wires for obvious damage or loose connectors (do not disconnect gas or electrical components). If wires are damp, allow to dry and then try a reset.

Notes for information to give to an engineer

1) Exact fault code and any cause number from the information menu (use the spanner/return button if you can access the info menu).

2) When the fault happened (during firing, after a short run, during heavy rain, after a power cut etc.).

3) Whether a single reset cleared it and whether it recurred, and any visual signs you saw (water, damaged cable, frayed insulation).

Diagnostic and repair steps a qualified Gas Safe engineer will typically follow

1) Confirm fault: read fault and cause codes from the boiler's information menu and log any lockout behavior.

2) Visual and electrical inspection: check the condition and routing of the ionisation/ignition electrode and cable, verify connectors are tight and insulation intact, check for moisture, contamination or soot on the electrode tip.

3) Measure ionisation current: use the correct diagnostic meter and procedure to measure ionisation current during and after burner operation to confirm a residual current exists when the gas valve is closed.

4) Check electrode assembly and lead: clean or replace the electrode/lead if contaminated, damp, cracked or damaged. Ensure correct electrode positioning and correct lead routing away from hot or damp areas.

5) Check earthing/insulation: verify PCB earths and insulation of signal wires to ensure no unintended current paths are present.

6) Check ionisation oscillator/PCB inputs: test the ionisation amplifier/oscillator circuit and the PCB input that monitors ionisation; repair or replace PCB if that is the confirmed fault.

7) Check the gas valve and combustion control: verify that the gas valve shuts cleanly and that the air-to-gas ratio control valve or related actuator is functioning correctly. Some false-flame faults can stem from valve leakage or control faults that allow a small residual flame or signal after shut off.

8) Run leak tests and functional tests: perform gas valve leak tests and full ignition/burner operation tests as per manufacturer guidance to ensure the fault is cleared.

9) Replace components only as required: common replacements for FA 306 are the ionisation lead/electrode assembly or, if proven faulty, the PCB or air-to-gas ratio valve. The engineer will replace the defective item and re-test.

10) Final checks and reset: after repairs the engineer will clear fault codes, run the boiler through several on/off cycles and confirm stable operation and correct ionisation readings.

Important cautions and final advice

1) FA 306 is a safety lockout designed to prevent unsafe operation. If a reset clears the fault temporarily but it returns, get a Gas Safe engineer to investigate – do not rely on repeated resets.

2) Do not attempt to replace gas valves, perform gas leak checks, or alter combustion settings unless you are a registered gas engineer. Working on gas appliances without the correct qualifications is dangerous and illegal.

3) Provide the engineer with the boiler model, serial number, exact error text and any photos you took. This speeds diagnosis.

4) If the boiler is under warranty or service plan, contact your installer or Worcester Bosch support and inform them of the FA 306 code.

If you want, tell me whether the fault returned after a reset, whether you saw any water/damage near the ignition electrode, and the exact model/serial if visible; I can suggest the most likely next part to check.