Ferroli A02 Fault Code
The A02 fault means the boiler successfully established a flame during ignition but lost it shortly afterwards — the ionisation probe stopped detecting the flame mid-cycle. This is distinct from A01, where ignition was never achieved at all.
What is the Ferroli A02 fault code?
The Ferroli A02 fault is triggered when the ionisation probe detects flame loss after a successful ignition. The boiler made a spark, gas was present, and a flame was established — but the ionisation probe's signal dropped to zero during the operating cycle. The PCB interprets this as a dangerous condition and locks out. A02 differs from A01 (no ignition at all) because ignition was momentarily successful. Common causes include a dirty or degraded ionisation probe that cannot maintain a stable signal, an intermittently sluggish gas valve that cannot sustain the required gas flow, combustion disruption from a partially blocked flue or condensate path, or a PCB input circuit fault.
What causes the A02 fault?
Combustion deposits gradually reduce the probe's ability to maintain a stable flame signal. The probe detects ignition but loses the signal seconds later, triggering A02. The most common cause.
An intermittently failing gas valve opens sufficiently for ignition but cannot maintain adequate gas pressure during the heating cycle. The flame starves and A02 is displayed.
A partially blocked flue creates backpressure that disrupts combustion air mid-cycle. The flame is established but extinguished by disrupted airflow.
A frozen condensate pipe creates backpressure in the condensate path, interfering with combustion and causing flame loss. A02 in winter often resolves by thawing the condensate pipe.
Cracked insulation or a loose ionisation probe connector can cause the probe signal to drop intermittently, triggering A02 even when the flame is still burning.
Rarely, the PCB's ionisation sensing circuit fails and generates false A02 readings. PCB diagnosis is by exclusion — after all other components test correctly.
What you can safely check yourself
Test another gas appliance. If it also has issues, the gas supply is the problem — call your gas supplier or check your prepayment meter.
In cold weather, pour warm water along the external condensate pipe. Once thawed, attempt one reset. A02 caused by condensate freezing resolves immediately on thaw.
If A02 returns on the next heating cycle, call a Gas Safe engineer. Resetting repeatedly without diagnosis does not address the underlying fault.
Do not reset the boiler more than once if the fault code returns immediately. Repeated resets without diagnosis can mask a worsening fault.
What needs a Gas Safe engineer
- Clean ionisation probe and test signal output — replace probe if signal remains unstable
- Test gas valve operation across the full heating cycle — not just at ignition
- Inspect ionisation probe wiring and connector for corrosion or loose contact
- Inspect flue terminal and condensate path for partial restriction
- Test gas inlet and manifold pressure under load
- Test PCB ionisation circuit if all other components pass
- Check burner assembly for carbon deposits affecting combustion
A02 from ionisation probe deposits is more frequent in South London hard water zones. Thames Water — supplying Wandsworth, Lewisham, Lambeth, Merton, Southwark, Greenwich, and Bromley — deposits calcium on combustion components, reducing ionisation probe sensitivity over time. Annual servicing includes a probe inspection and clean, which prevents A02 from developing. Winter A02 callouts across South London are also frequently caused by frozen condensate pipes — Reion recommends insulating external condensate runs on all Ferroli boilers.
How much does a A02 repair cost?
Costs below are UK averages. Reion provides a fixed quote after the £80 diagnostic visit — no obligation to proceed.
How to reset a Ferroli boiler showing A02
Confirm there is no gas smell — if you smell gas, do not reset. Leave and call 0800 111 999.
In winter, check and thaw the condensate pipe first.
Press the reset button for 3 seconds.
Monitor for flame loss within the first 60 seconds of operation.
If A02 returns within two heating cycles, call a Gas Safe engineer.
Ionisation probe replacement is one of the lower-cost Ferroli repairs — typically £80–£160 all in. Gas valve replacement is more significant at £260–£440, and Ferroli gas valves may carry a 3–7 day lead time. On a unit over 8 years old where the diagnosis is a PCB or gas valve, Reion will provide a repair-vs-replace comparison at the diagnostic visit.
Common questions about the Ferroli A02 fault
What is the difference between Ferroli A01 and A02 fault codes?
Can a Ferroli A02 fault be caused by cold weather?
How long does a Ferroli A02 repair take in London?
Is a Ferroli A02 fault an emergency?
Why does my Ferroli show A02 but it seemed to light at first?
Other Ferroli fault codes
Need a Ferroli engineer in London?
Reion is Gas Safe registered (919881), based in South London, and available 24/7. Fixed price after the diagnostic visit — no hidden charges.
