Error L6

Safety first: if you smell gas, evacuate the property, do not operate electrical switches or the boiler, and call the gas emergency number immediately. If you suspect carbon monoxide (unusual soot, yellow rather than blue flame, illness), turn off the appliance, ventilate windows, leave the building and call the appropriate emergency services. Do not attempt internal repairs involving gas, burners, electrodes or the PCB — these must be done by a Gas Safe / registered engineer.

Initial checks a homeowner can do:

1) Note the fault: write down L6 and any other codes or lights shown, and when the fault started. Take a clear photo of the boiler display if possible. This speeds up an engineer diagnosis.

2) Reset the boiler: follow the manufacturer instructions. Press the RESTART button and allow the ignition sequence to run. If that does not work, isolate mains power to the boiler for about 30 seconds and restore power, then try restart again. Only attempt a couple of resets; repeated resets that do not clear the fault are a sign you need a professional.

3) Check the gas supply: confirm other gas appliances in the house work (hob, gas fire). If none are working, check the meter and any isolation valve. Do not try to force or alter gas valves.

4) Check obvious external blockages: inspect the flue terminal outside for nests, debris or blockage and clear anything obvious and safe to remove. Also check external condensate/termination pipes for ice or blockages. Do not dismantle the flue.

5) Check basic electrics: ensure the boiler has mains power and external controls (programmer, room thermostat) are calling for heat. If the boiler display shows only L6 with no other symptoms, that supports a flame detection fault rather than pressure or pump issues.

What a professional will check and why you should call one:

1) Flame detection electrode condition and position: the engineer will isolate the boiler, remove the cover and inspect/clean/replace the ignition/flame detection electrode and the high tension lead. Incorrect electrode position, carbon build-up or a damaged lead commonly causes false signals.

2) Flame signal and earth continuity: using diagnostic tools the engineer will measure the flame sensing voltage/current and earthing of the appliance. Poor earthing or a degraded signal can produce false flame warnings.

3) Wiring and connectors: the engineer will check the flame-sensing wiring and connectors for corrosion, loose connections, damp ingress or damage and repair as required.

4) Control PCB and electronics: if electrode and wiring are good the control board or its software may be at fault. Engineers can test and, if necessary, replace the PCB or fascia electronics.

5) Ancillary causes: the engineer will also rule out intermittent gas supply issues, ignition faults, or other error codes that might be linked to the L6 event.

When to call a Gas Safe / registered engineer:

1) If the L6 code persists after a sensible reset and power cycle. 2) If you have any doubt about gas smell or unusual combustion behaviour. 3) If the boiler has been opened or worked on recently, or if there has been water ingress or electrical surges. Provide the engineer with the boiler model (Keston S30), serial if available, the exact fault code (L6) and anything you observed during your checks.

Other practical notes:

- Do not remove the boiler cover or tamper with the burner, electrodes, gas valve or PCB unless you are a qualified engineer. Doing so is dangerous and may invalidate warranties.

- Keep a record of fault occurrences, resets attempted and any conditions (e.g. weather, power cuts) that preceded the fault; this helps the engineer diagnose intermittent issues.

- If the boiler is under warranty, contact Keston support first; otherwise book a Gas Safe registered engineer. Provide them with all the information you collected so they can attend prepared.