Error F.1

Safety precautions:

- If you smell gas (rotten egg/mercaptan odor) evacuate immediately, do not operate electrical switches, open windows and call the gas emergency number from a safe location. Do not attempt to relight the boiler.

- Before doing any checks, switch the boiler to the off position and allow it to cool. Do not remove sealed panels or attempt to access internal gas/ignition components unless you are Gas Safe qualified.

- Do not attempt to adjust the gas valve, replace electrodes, or test live gas circuits yourself.

Initial homeowner checks (safe, non-invasive):

1. Check other gas appliances in the house (hob, oven) to see if they are working. If none of them work, the issue is likely a supply/problem upstream and you should contact your gas supplier.

2. Confirm the boiler’s gas isolation valve (usually a lever on the boiler gas pipe) is in the open position. If it has been turned off accidentally, open it and try a reset.

3. Reset the boiler following the user manual instructions (use the boiler’s reset control). If the boiler re-ignites and runs, monitor for reoccurrence. If it immediately returns to F.1 or locks out repeatedly, stop and call an engineer.

4. Check the flue terminal outside for obvious blockages (nests, debris). Do not crawl into confined spaces or attempt internal flue work yourself. A blocked flue can prevent combustion air/venting and cause ignition failure.

5. In very cold weather check externally routed condensate pipes for freezing or blockage; thawing may allow the boiler to restart.

If the simple checks don’t clear the fault, call a Gas Safe registered engineer. Typical professional diagnostic and repair steps (for the engineer):

1. Confirm the fault history and number of lockouts. Inspect the boiler for visible signs of water ingress, corrosion or damage to ignition wiring and connectors.

2. Verify gas supply and inlet pressure at the boiler. Check the gas meter and upstream isolation/regulator. Restore any interrupted supply in coordination with the supplier if required.

3. Check ignition sequence: observe spark generation, flame sensing and flame signal. Inspect and if necessary clean/replace the ignition electrode(s) and check/replace ignition leads. Check electrode gap and alignment according to Vaillant specifications.

4. Test the ignition transformer/spark generator and measure ignition lead continuity. Check the flame detection circuit and electrode earth/continuity.

5. Test the gas valve operation and associated wiring. Measure gas valve coil resistance (manufacturer guidance suggests around 50–54 ohms for some valves — engineer to use official service data). If the gas valve or harness is faulty replace as required.

6. Inspect the PCB and ignition control circuits for faults or moisture; test eBUS/communication faults if present. Replace or repair PCB only with correct parts and settings.

7. Check flue and pressure switches (including fan operation if applicable) to ensure correct combustion air flow and no recirculation or blockages.

8. After repairs, carry out combustion and gas-tightness tests, confirm correct gas valve setting and safe operation, and run the boiler through several ignition cycles to confirm reliability.

Final notes:

- F.1 is a lockout caused by failed ignition; it often needs professional diagnosis and repair. Do not attempt internal repairs unless you are qualified and registered.

- If the boiler repeatedly locks out after a short fix or reset, stop using it and book a Gas Safe engineer. Continued attempts to force operation can be unsafe and may mask the underlying fault.

- Always use a Gas Safe registered engineer for anything involving gas valves, burner parts, ignition systems, or internal PCB/electrical repairs.