Ferroli A02 Fault Code: Causes, Fixes & Repair Costs
What does the Ferroli A02 fault code mean?
The A02 code is a hard lockout fault on Ferroli boilers, meaning the boiler has shut itself down and will not restart until you manually reset it. It indicates that the flame sensor (ionisation electrode) is reporting a flame signal at a point when the burner has not been instructed to fire. Because an unexpected flame signal is a genuine safety concern, Ferroli's control system immediately locks the boiler out. This is quite different from a simple ignition failure — the boiler isn't struggling to light; it believes a flame exists when it shouldn't. Codes beginning with 'A' on Ferroli boilers are always hard lockouts of this type, whereas 'F' prefix codes are softer blocking faults that can sometimes clear on their own.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Faulty or contaminated ionisation electrode Common
The ionisation electrode is the sensor that detects whether a flame is present. If it becomes coated with carbon deposits or oxidation, or if it is cracked or misaligned, it can send a spurious 'flame present' signal to the PCB even when the burner is off. This is the single most common reason for an A02 lockout and is often resolved by a Gas Safe engineer cleaning or replacing the electrode.
- PCB (printed circuit board) fault Sometimes
The control board interprets the signal from the ionisation electrode. If the PCB itself is faulty — due to component failure, moisture ingress, or age — it may incorrectly register a flame signal regardless of what the electrode is actually reading. PCB faults become more likely on boilers that are several years old or have been subjected to damp conditions.
- Wiring or earthing problem Sometimes
Poor earthing on the boiler's electrical supply, or damaged and chafed wiring between the ionisation electrode and the PCB, can introduce stray electrical signals that mimic a flame detection reading. This cause is sometimes overlooked but is worth checking, particularly in older installations or where recent electrical work has been carried out nearby.
- Low or unstable electrical supply to the ignition circuit Rare
An inadequate or fluctuating mains supply can result in the ignition and flame-sensing circuitry behaving erratically, producing invalid flame signals. While less common than a faulty electrode or PCB, it is worth ruling out if other checks draw a blank.
How to fix it
- Reset the boiler once DIY safe
Locate the reset button on your Ferroli boiler — it is usually marked with an 'R' or a flame symbol. Hold it for approximately 5–10 seconds. If the boiler fires up and runs normally, monitor it closely over the next hour or two. A single reset after a one-off glitch is reasonable, but do not reset the boiler more than two or three times in total if the A02 code keeps reappearing — repeated resets will not fix an underlying fault and could cause further damage.
- Check your gas supply is live DIY safe
Make sure your gas meter isolation valve is fully open and that other gas appliances in your home (such as a hob or gas fire) are working normally. If there is a wider gas supply issue, contact your gas supplier. Do not attempt to interfere with any gas pipework or valves beyond the main meter isolation valve.
- If the fault returns, stop resetting and call a Gas Safe registered engineer Gas Safe engineer
A recurring A02 code points to a genuine component fault — most likely the ionisation electrode or the PCB — that requires professional diagnosis. A Gas Safe engineer will test the electrode for continuity and contamination, inspect the wiring and earth connections, and assess the PCB. Do not continue to reset the boiler in the hope the fault clears; an unexpected flame signal is a safety-related lockout and must be properly investigated.
- Engineer to test and clean or replace the ionisation electrode Gas Safe engineer
With the boiler fully isolated, the engineer will remove and inspect the ionisation electrode. If it is heavily carbonised or physically damaged, it will be cleaned or replaced. This is the most straightforward and cost-effective repair for an A02 fault and resolves the majority of cases.
- Engineer to inspect PCB and wiring if electrode is not the cause Gas Safe engineer
Should the electrode test satisfactorily, the engineer will examine the wiring harness for damage, check earth continuity on the electrical supply, and test the PCB. A faulty PCB will need to be replaced — a more involved and costly repair, but one that restores full boiler function when it is the root cause.
Parts you may need
- Ionisation / ignition electrode · from £25
- Electrode lead / ignition cable · from £18
- PCB (control board) — Ferroli compatible · from £120
- Electrode gasket / seal · from £8
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £100–£320, depending on the underlying cause.
Frequently asked questions
Is the Ferroli A02 fault dangerous?
It is treated as a safety lockout because the boiler's sensor believes there is a flame when there shouldn't be. The boiler correctly shuts itself down in this situation, so you are not at immediate risk. However, you should not keep resetting the boiler and ignoring the code — have a Gas Safe engineer diagnose the cause promptly. If at any point you smell gas, leave the property, avoid operating electrical switches, and call the National Gas Emergency Service on 0800 111 999.
Can I fix the Ferroli A02 fault myself?
The only homeowner-safe action is a single manual reset. The components involved — the ionisation electrode, PCB, and associated wiring — must be inspected and replaced by a Gas Safe registered engineer. Working on these parts yourself is not only unsafe but would also invalidate your boiler warranty and potentially your home insurance.
How much does it cost to fix an A02 fault on a Ferroli boiler?
For most people, the repair falls between £100 and £320 including parts and labour. An electrode clean or replacement is at the lower end of that range (roughly £100–£150), while a PCB replacement typically costs £220–£320 all in. In rare cases where multiple components need attention, costs can climb higher — if your boiler is over ten years old and the repair quote is approaching £400 or more, it may be worth comparing that against the cost of a new boiler.
Why does my Ferroli keep showing A02 after I reset it?
If the A02 code returns quickly after each reset, the underlying fault has not cleared — most likely the ionisation electrode is faulty or contaminated, or the PCB has developed a fault. Repeated resets will not resolve either of these issues and may cause additional wear. Book a Gas Safe engineer visit rather than continuing to reset the boiler.