Error F2, FN or LN

Safety precautions:

- If you smell gas (rotten egg smell) leave the building immediately, do not operate electrical switches or the boiler, shut off the gas supply at the emergency control if you know how and it is safe to do so, and call the gas emergency number for your area.

- If you suspect a blocked flue or carbon monoxide (staining, excessive soot, exhaust smells), turn the appliance off, ventilate the area, do not use the boiler or other gas appliances, and call a Gas Safe engineer immediately. Carbon monoxide risk is serious.

- Do not remove covers or attempt internal repairs unless you are a Gas Safe registered engineer. Internal work on gas appliances is dangerous and illegal for unqualified persons.

Initial checks a homeowner can do (safe, non-invasive):

1. Note the exact fault code and any pattern (when it happens, after how long, weather conditions). This helps the engineer.

2. Check other gas appliances (hob, cooker, gas fire). If they do not work, the problem is likely a gas supply issue—contact your gas supplier or check your prepaid meter balance.

3. Check the boiler’s gas isolation tap at the meter or near the boiler to ensure the tap is on (only if you know where and it’s safe to check).

4. Attempt a boiler reset: follow the manufacturer’s reset procedure or switch the boiler off at the fused spur, wait 10 seconds, and switch back on. If the F2 returns immediately or repeatedly, stop and call an engineer.

5. Check central heating pressure on the boiler gauge (this is the heating system water pressure, typically about 1–1.5 bar cold). Note it by taking a photo. Low system pressure can stop normal operation, but an F2 is usually combustion-related rather than CH pressure.

6. Visually inspect the flue terminal outside for obvious blockages (nests, leaves, moss) if it is safely accessible from ground level. Do not climb to reach a high flue; leave that to an engineer.

7. If the weather has been very cold, check the condensate pipe (usually a small plastic pipe that runs to outside or into a drain). If it is frozen, thaw it gently with warm water or a hot towel; do not use open flame. Insulate the condensate pipe afterward to reduce re-freezing.

Specific diagnostic and fix steps (what to try and what must be left to an engineer):

- Condensate pipe frozen or blocked: If you can access the external run safely and it is frozen, pour warm (not boiling) water along the run and the outside stub to thaw it. Once thawed, try resetting the boiler. If the condensate trap inside the boiler is suspected blocked, do NOT remove internal parts unless you are qualified—call an engineer.

- Gas supply checks: If other gas appliances don’t work or you’re on a prepaid meter, top up or contact the supplier. If you switch the gas back on at an isolation valve, use the reset procedure on the boiler. If gas is present to other appliances but the boiler still faults, it points to a boiler internal issue (valve, ignition, detection).

- Flue obstruction: If you found a clear, ground-level blockage and can safely remove it, do so and then reset the boiler. If the flue is high or removal requires working at height, stop and call an engineer.

- Reset and observe: After any safe intervention, reset the boiler and watch the ignition sequence. If the boiler tries to light and then locks out with F2 again, record whether it fails immediately or after running briefly; that timing helps diagnosis.

- What you must not do: do not try to dismantle gas valves, burners, fan assemblies, ignition electrodes, or the PCB. Do not attempt electrical measurements or adjustments on gas components unless you are trained and registered.

When to call a Gas Safe engineer:

- If basic safe checks (meter/credit, condensate thaw, simple reset, visible flue clearing) do not cure the fault.

- If gas supply to the household is fine but the boiler still shows F2/FN/LN.

- If the fault repeats, occurs intermittently, or follows work on the system.

- If you suspect a faulty gas valve, fan, ignition electrode, flame sensor, internal condensate/trap blockage, or any wiring/component fault. These require specialist diagnostic equipment and competent replacement.

Information to give the engineer when you call:

- Exact fault code shown (F2, FN, LN) and any other codes, whether the code is continuous or intermittent, what you have already checked (meter, reset, condensate thaw, flue check), and whether other gas appliances are working.

Final note:

F2/FN/LN indicates a combustion/ignition safety issue. Some homeowner checks can clear simple problems (no gas, frozen condensate, blocked external flue). However, because the fault can be caused by dangerous failures (gas valve, fan, flame detection), if you cannot clear it with the safe steps above you must stop and call a Gas Safe registered engineer. Do not attempt internal repairs yourself.