Error 306 V

Safety precautions:

1) If you smell gas or suspect a leak: do not operate electrical switches or the boiler. Turn off the gas supply at the meter if it is safe to do so, evacuate the property, and call the national gas emergency number immediately. Do not attempt internal repairs.

2) If there is no smell of gas, isolate the boiler electrically (switch off at the fused spur) before attempting any internal visual inspection. However, do not open sealed parts or attempt to work on gas valves, the burner, or internal electrical components unless you are Gas Safe registered.

3) Keep the area ventilated and do not use the boiler until a competent engineer has confirmed it is safe.

Initial homeowner checks (safe, non-intrusive):

1) Note the exact error code and when it occurred (time, what the boiler was doing: heating, hot water, start-up, shutdown). This information will help the engineer.

2) Try a simple reset: press and hold the boiler reset button for about 3 seconds (follow your manual if slightly different), then allow the appliance to attempt restart. If the fault does not reappear, monitor the boiler for recurrence. If it returns, proceed to call a professional.

3) Check for obvious signs of water ingress, soot, or debris around the flue and burner area (outside the sealed casing) and ensure the room ventilation/air supply to the boiler is not blocked.

4) Look (without removing panels) for wet or visibly damaged wiring to the outside of the boiler casing and for any obvious loose connectors on accessible terminal blocks. Do not pull on wires or open the burner compartment.

5) If the ionisation electrode lead is routed externally and clearly visible (and you are competent to do a visual check without opening the boiler), look for fraying, chafing, or moisture on the lead or connector. Do not disconnect or reconnect live terminals.

Diagnostic steps and likely fixes (to be performed by a Gas Safe engineer):

1) Verify flame monitoring circuitry: the engineer will measure ionisation current/voltage to confirm whether the electrode/cable is producing a false signal. A damaged ionisation electrode or lead is a common cause and is often replaced if faulty.

2) Check the air/gas ratio control valve and associated mechanism: FA 306 commonly points to the air/gas ratio control valve behaving incorrectly (sticking or not fully closing) so it may allow conditions that create a flame signal after fuel shut-off. The valve may need adjustment, cleaning, repair or replacement.

3) Test the gas valve(s) for leakage or proper shut-off: the engineer will carry out leak checks and electrical checks on the modulating/EV gas valves. If a valve does not seal fully or the feedback circuit is wrong, the control can register a flame condition after shutdown.

4) Inspect the burner and flue path: ensure there is no residual burning, soot issues, or flue/ventilation problems affecting combustion stability and detection.

5) Check control electronics and connectors: the control PCB, code plug and connectors are inspected for faults, corrosion or damaged wiring that could cause incorrect flame feedback.

6) After any component replacement or adjustment, the engineer will run commissioning and safety checks: verify correct ignition, modulation, safe shut-down, and that flame detection is reliable across operating range.

When to call a professional (and why):

1) If reset does not clear the fault permanently, or if the fault comes back repeatedly, book a Gas Safe registered engineer. FA 306 involves fuel control and flame monitoring—work that legally and practically requires a qualified gas engineer.

2) If you find any damaged ignition/ionisation leads, any evidence of gas smell, or leaking components, stop using the boiler and contact a Gas Safe engineer immediately.

Final notes: do not attempt to replace the air/gas ratio control valve, gas valves, ionisation electrode or perform electrical repairs yourself unless you are a qualified Gas Safe engineer. Keep a record of the fault occurrences and any simple actions you have already taken (reset, time/date, operating mode) to give to the engineer; it will speed diagnosis and repair.