Error FA 306

Safety precautions:

1) If you are not confident working near gas or live electrical parts, stop and call a Gas Safe engineer. Only a Gas Safe engineer should work on gas valves, ignition systems or internal boiler wiring.

2) Before any internal inspection, isolate the boiler by switching off the mains electrical supply at the isolator and, if you will touch gas components, ensure the gas supply is isolated by a qualified engineer.

3) Do not block ventilation or flues and do not attempt to force a boiler to run if it’s in lockout.

Initial checks a homeowner can do:

1) Note the exact error code (FA 306), model and serial number, and when it started. This information helps the engineer.

2) Try a single reset of the boiler: press and hold the reset button for 3 seconds (or follow the model-specific reset method in the manual). Wait and observe if the boiler starts and runs normally. If the fault clears and does not return, monitor the boiler; if it returns, follow the steps below.

3) Check mains power to the boiler and home, and ensure the boiler hasn’t had recent power interruptions. Check that the boiler water pressure is within the normal range (typically around 1–1.5 bar cold) — low pressure usually causes different faults but is quick to rule out.

4) Check the external visible areas: ensure the flue terminal is not blocked, condensation drain/condensate traps are not frozen or blocked, and that nothing obvious is wet or heavily sooted around the boiler front that could affect the electrode area.

Specific diagnostic and basic fix steps (only non-invasive tasks unless you are qualified):

1) Visual inspection of the ignition/flame sensing electrode and leads: with the boiler isolated from mains power, open the outer casing only if you are comfortable and it is safe to do so. Inspect the ignition/ionisation electrode, its ceramic insulator and the lead for obvious damage, heavy soot, corrosion or moisture. Check connectors for secure seating. If you see minor contamination or moisture, the electrode can sometimes be dried and gently cleaned with a clean, dry cloth once power is off. Do NOT bend or clamp the electrode or use abrasive materials. If you are unsure, stop and call a professional.

2) Drying out: if the electrode area or ionisation cable looks damp (condensate, plumbing leak, or flue condensation), allow the area to dry. You can leave the casing open for a short while with power off to help evaporate moisture, then reassemble and test with a reset.

3) Tighten and reseat connectors: with the power off, check the plug connections to the ignition electrode and the PCB - unplug and re-plug carefully if accessible and you are confident. Corroded or loose connections can cause false signals.

4) Single reset and observe: after reassembly, turn power back on and reset once. Watch the boiler through a full ignition cycle if it’s safe to do so. Note whether FA 306 appears immediately, during run, or after burner stop. Record timing for the engineer.

5) If the fault only appeared once and does not return after checks and drying, you can monitor the boiler. If it reappears, turn the boiler off and arrange engineer attendance.

When to call a professional and what they will check:

1) Call a Gas Safe registered engineer if the code persists after a reset and the simple visual checks above. Give them the error code FA 306, the boiler model and serial, and what you already tried.

2) The engineer will perform safe live diagnostics: measure the ionisation current, check continuity and insulation of the ionisation cable, test the ignition/flame probe and its position, test the gas valve for leakage or sticking (EV1/EV2), inspect the air-to-gas ratio control valve, and check the burner control unit / PCB and any burner control modules (KIM/burner control unit) for faults.

3) Typical professional fixes include replacing a damaged ionisation cable or electrode, servicing or replacing the gas valve or air/gas control assembly, repairing or replacing faulty wiring or PCB components, and addressing any debris, sooting or flue/combustion issues causing false signals.

Important reminders:

1) Do not attempt to replace or adjust the gas valve, gas injector or perform any gas-side repairs yourself. These are controlled works requiring Gas Safe registration.

2) Avoid repeated resets. One reset to test is reasonable; repeated resets mask the underlying fault and can be unsafe.

3) Provide the engineer with a clear description of the fault pattern (when FA 306 occurs, whether after burner stop, after DHW or CH demand, after a power flicker, etc.) and any recent work, weather conditions (very cold causing frozen condensate), or smells. This speeds diagnosis.

If you need immediate help and are uncertain of safety (smell of gas, persistent lockouts, or visible gas or electrical faults), turn the boiler and gas supply off, ventilate the area and contact your gas emergency line or a Gas Safe engineer immediately.