Error F0

Safety precautions:

1. If you smell gas (rotten egg smell) or suspect a gas leak, evacuate the property immediately, do not operate electrical switches, do not use phones inside the property, and call the gas emergency number for your country right away.

2. If in doubt about any step, stop and call a Gas Safe registered engineer. Do not remove the boiler casing or attempt internal electrical or gas repairs yourself.

3. Before performing any basic checks, switch off the boiler using the external on/off switch and, if you can safely do so, isolate electrical power to the boiler at the fused spur. Do not isolate the gas unless you are certain how to do it safely.

Initial checks a homeowner can safely do:

1. Check for obvious signs: look for water under the boiler, scorch marks, loose wires visible outside the casing, or burning smells. Note these for the engineer.

2. Verify the boiler has power: check the fused spur or wall switch and the household fuse box. If other electrics on the same circuit are dead, restore power before further checks.

3. Check the boiler pressure gauge. If pressure is extremely low or zero, that can cause lockouts (although F0 is usually internal). Re-pressurise only if you know how and the system is cold; otherwise wait for an engineer.

4. Read the display and information menu: press the spanner/return or info button to see any static cause codes that accompany F0 (some models show a cause number that helps a technician).

Safe reset procedure (do first):

1. Locate the reset button on your CDi Classic (or follow manual instructions). Press and hold the reset button for 3 seconds then release. Wait for the boiler to attempt restart.

2. If F0 remains, try the extended reset sequence described in some manuals: press reset for 10 seconds, release, wait 30 seconds and press again to clear. If this clears and the boiler runs normally, monitor for recurrence and book a service as the fault may return.

Further homeowner diagnostics (visual and non-invasive):

1. Check visible connectors and leads outside the casing (e.g., control cables to room thermostats or external controls) are seated and undamaged. Do not open the boiler casing to inspect internal wiring.

2. Note whether any other fault codes appear, whether the fault is constant or intermittent, and whether it follows power cuts, storms, or recent work on the heating system. Record what you see for the engineer.

What to tell a Gas Safe engineer / next steps if reset fails or fault recurs:

1. If the F0 persists after reset, arrange for a Gas Safe registered heating engineer to attend. Tell them the boiler model, the F0 code, any displayed cause code from the info menu, and results of your basic checks.

2. The engineer will perform safe, technical diagnostics: check ignition leads and electrode, test ionisation/flame sensing circuits, check gas valve EV1/EV2 for leak tests, inspect the PCB and connector contacts, verify code plug and programmer interface, and check sensors and wiring. They may use service menus, scope meters and leak tests only a qualified engineer should perform.

3. If a gas valve leak or other safety-critical fault is suspected, the engineer will isolate gas, repair or replace defective parts, and perform safety tests before returning the boiler to service.

Important final notes:

1. Because F0 indicates an internal control/electrical fault and can involve gas valve safety, it is not something to attempt to repair yourself. Use only a Gas Safe registered engineer for any internal work, gas valve checks, PCB replacement or ignition system repairs.

2. If the boiler has been reset and runs, still arrange a service appointment. Intermittent internal faults often precede component failure and should be investigated to avoid future loss of heating or unsafe conditions.