Error C0

Safety precautions:

1. Before doing anything, ensure your own safety: isolate the electrical supply to the boiler at the fused spur or consumer unit if you will remove the boiler cover or access internal electronics. Do not work on live electrical circuits. If you are not competent with electrical work, do not open the boiler.

2. If you suspect a gas issue (smell of gas, other appliances not working), turn off the gas at the meter and call your gas supplier and a Gas Safe/registered engineer immediately. Do not attempt internal repairs.

3. Take photos of any connectors or the chip card location before disconnecting anything so you can reseat correctly. Keep clear of hot components if the boiler was recently running.

Initial homeowner checks (non-invasive):

1. Check the boiler display and note the exact message. Try pressing the Restart button once as directed by the manual. Wait for the ignition sequence. If the display changes or the boiler starts, monitor for normal operation.

2. Confirm mains electrical supply to the boiler is present: check other powered devices, check the boiler fused spur or MCB is on, check for a blown fuse in the spur. If the display is blank or unstable, address the electrical supply first.

3. Confirm external controls are calling for heat: check the programmer/timer is set to call for heating/hot water and any room thermostat or cylinder thermostat is on and set high enough.

4. Check system water pressure (if the boiler has a pressure gauge). Ensure pressure is in the normal range (approx 1.0–1.5 bar cold for most systems). Low pressure can create unrelated faults; refill/pressurise if needed per your manual and then press Restart.

5. Check other household gas appliances to confirm a gas supply is available. If none work, check the gas meter/prepayment status before proceeding.

Diagnostic and specific steps (only proceed if competent and after isolating mains power when instructed):

1. Simple power-cycle: with the mode knob set to BOILER OFF, switch off the boiler electrical supply at the fused spur or consumer unit. Wait 30–60 seconds, restore power, set mode to BOILER ON and press Restart. Observe the display and any change in the fault code.

2. If C0 persists, try a second restart. The manual advises restarting once or twice; repeated resets can trip lockouts (L5) so avoid excessive resets in short time.

3. Visual external inspection: with panel closed and power on, check that there are no obvious error messages about mains voltage or PCB faults. Verify the burner-on lamp behaviour during attempts to start. Note any other codes (F9, F0, etc.) which indicate PCB or sensor faults.

4. Reseat the Boiler Chip Card (only if you are competent and have isolated the mains): turn off the electrical supply, remove the boiler fascia/cover per the manual, locate the BCC and carefully remove it and inspect for corrosion, bent contacts, damage or foreign objects. Clean contacts gently if dirty (use contact cleaner from a reputable brand) and reseat firmly, ensuring it sits fully in the connector. Replace the cover, restore power and attempt a restart. If unsure how to access the card, stop and call an engineer.

5. If the BCC is missing or visibly damaged, it should be replaced with the correct, manufacturer-specified chip card. This replacement and any firmware/configuration often requires an authorised part and may need programming or configuration by Keston or a Gas Safe engineer. Do not fit non-original or unknown cards.

6. If reseating or replacement of the card does not clear C0, or if the card appears OK but the PCB reports other errors (F9, PCB fault, unconfigured PCB), the problem is likely a faulty control PCB, a communication fault between PCB and card, or an internal wiring fault. These faults require diagnostics with the correct test equipment and replacement components and should be handled by a qualified engineer.

7. If the boiler is under warranty, or if you are not a qualified installer, contact Keston technical support or your installer. If out of warranty, contact a Gas Safe registered engineer (or RGII in Ireland). Tell them the exact fault code (C0) and what you have already checked (power-cycle, reseated card, pressure, external controls).

When to call a professional and what they will do:

1. Call a Gas Safe registered engineer (or official Keston service while under warranty) if the restart and reseating do not clear the fault, if you find a damaged or missing BCC, if the PCB reports additional faults, or if you are not confident to access the card safely. Do not attempt to change or repair the PCB, gas train, or any internal electrical parts yourself.

2. The engineer will isolate and safely open the appliance, test electrical supply and PCB communications, check and if necessary replace/program the BCC, test and potentially replace the control PCB, verify wiring and connectors, and run full safety checks including gas tightness and flue/combustion checks before returning the boiler to service.

Final notes:

1. The C0 fault is often resolved by a qualified engineer reseating or replacing the BCC or addressing a PCB/configuration issue. Homeowners should limit activity to non-invasive checks, simple restarts, confirming external controls and pressures, and safely reseating the card only if competent and after isolating mains.

2. Keep the boiler serial number, model, and any warranty details to provide to Keston or the engineer when you call, and avoid repeated resets which may escalate lockout conditions.