Ferroli A26 Fault Code: Causes, Fixes & Repair Costs
What does the Ferroli A26 fault code mean?
The A26 code is a manual-lockout fault — the 'A' prefix on any Ferroli fault code means the boiler has shut itself down and will not restart until you physically press the reset button. Specifically, A26 indicates that the boiler's control board (PCB) has detected that one or more of its internal operating parameters are incorrect or have become corrupted. Rather than attempt to fire up in an unknown state, the boiler locks out as a safety precaution. Related parameter-fault codes on Ferroli boilers include A23, A24, A54, A55, and A63 — if your display shows any of these, the diagnosis and approach are broadly the same as for A26. By contrast, codes beginning with 'F' (such as F15, F21, F40, F47, F50, F51, F53) are 'blocking' faults that may clear on their own; A-prefix codes will not.
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
- Corrupted or incorrectly set PCB parameters Common
The most frequent trigger. A power cut, voltage spike, or firmware glitch can cause the values stored in the PCB's memory to be reset to a default or invalid state. The boiler detects this mismatch and locks out. On many Ferroli models — particularly the Optimax range — the fix can be as simple as navigating the parameter menu on the control panel and correcting a single value (see steps below).
- PCB internal fault or component failure Sometimes
If the parameter settings look correct but the fault persists, the control board itself may have developed a fault — a failed capacitor, a damaged relay, or general component degradation. This is more likely on older boilers or units that have experienced repeated power surges. The board will need testing with a multimeter by a Gas Safe engineer before condemning it.
- Loose or damaged wiring to the PCB Sometimes
A break or poor connection in the wiring loom feeding the control board can cause the PCB to behave erratically and register a parameter error. This is worth checking before replacing the board, as a re-wire is considerably cheaper than a new PCB.
How to fix it
- Attempt a parameter correction via the control panel (Optimax and similar models) DIY safe
On certain Ferroli models, particularly the Optimax range, a single parameter change clears this fault without any parts. The reported method is: hold the reset button down until the display shows 'T5', then press reset once more (the display should show 'P01'). Use the heating temperature button to scroll to 'P02', then press the hot water temperature button until the value changes to '2'. This takes around 30 seconds. Check your specific model's manual to confirm the procedure applies to your boiler before attempting it. If in doubt, skip this step and call an engineer.
- Reset the boiler DIY safe
Locate the reset button — usually marked with an 'R' or a flame symbol. Hold it for approximately 5–10 seconds and see whether the boiler fires up normally. If the A26 code reappears, attempt the reset no more than two or three times in total. Repeatedly forcing a lockout-protected boiler to restart risks damaging the heat exchanger or fan, turning a cheap fix into an expensive one.
- Check for an obvious power supply issue DIY safe
Make sure the boiler's fused spur is switched on and that your home hasn't lost power to the circuit. A power cut or significant voltage fluctuation is a common trigger for PCB parameter corruption, so it is worth confirming the supply is stable before calling an engineer.
- Call a Gas Safe registered engineer to test the PCB and wiring Gas Safe engineer
If the fault returns after resetting or the parameter correction does not apply to your model, you need a Gas Safe engineer. They will use a multimeter to test the wiring loom for breaks or poor connections — a straightforward re-wire is far cheaper than a new board. If the wiring is sound, the engineer will assess whether the PCB can be reprogrammed or whether it needs replacing. Never replace the PCB without first ruling out a simple parameter or wiring fix.
Parts you may need
- Ferroli PCB (control board) · from £180
- Wiring loom / harness · from £45
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 £80–£350, depending on the underlying cause.
Frequently asked questions
Can I fix Ferroli A26 myself without calling an engineer?
Possibly, yes — for certain models. The A26 fault is unusual in that a parameter reset through the control panel (not involving any gas components) resolves it on many Ferroli Optimax boilers. If you can follow the T5-to-P02 menu procedure described in the steps above and it matches your model's manual, this is a legitimate homeowner fix. However, if the fault returns or the procedure does not apply to your boiler, you will need a Gas Safe engineer to inspect the wiring and PCB.
How much does it cost to fix a Ferroli A26 fault in the UK?
If an engineer visit and a parameter reset or minor wiring repair resolves it, expect to pay £80–£150 for diagnosis and labour. A full PCB replacement typically costs £200–£350 including parts and labour for most Ferroli models. On some discontinued or older ranges, the PCB alone can cost over £300 before labour is added — in those cases, if your boiler is more than 10 years old, it is worth getting a new boiler quote at the same time, since repair costs can approach the threshold where replacement makes more financial sense.
What is the difference between an 'A' fault code and an 'F' fault code on a Ferroli boiler?
On Ferroli boilers, codes prefixed with 'A' (such as A26, A23, A24) are hard lockouts — the boiler will not restart without a manual press of the reset button. Codes prefixed with 'F' (such as F15, F21, F40) are blocking faults that may clear automatically once the underlying condition resolves. A26 is therefore more serious in the sense that it will never self-recover, but it does not necessarily mean the repair is expensive.
Why does my Ferroli keep showing A26 even after I reset it?
If the A26 fault returns every time you reset the boiler, the underlying cause has not been resolved. The most likely explanation is either that the PCB parameters have not been corrected (try the parameter menu procedure if it applies to your model), or that the control board has a genuine hardware fault or there is a wiring issue causing repeated corruption. At this point, further resets will not help and could mask a developing problem — contact a Gas Safe registered engineer for a proper diagnosis.