Ferroli A34 Fault Code: Causes, Fixes & Repair Costs
What does the Ferroli A34 fault code mean?
The A34 fault code appears on Ferroli boilers when the control board detects that the incoming mains electrical supply voltage has dropped below the minimum acceptable threshold — typically under 170–180V. When this happens, the boiler locks out as a precautionary measure to prevent damage to internal components. The fault is essentially the boiler telling you it cannot operate safely on the voltage it is currently receiving. Related electrical supply codes on Ferroli boilers include A35, A36, and A62, which cover other voltage and electrical component faults — if your display shows one of those, the underlying checks are similar.
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
- Low or unstable mains supply voltage Common
The most frequent trigger. If the voltage reaching the boiler dips below roughly 170–180V — whether due to a local supply problem, high demand on the circuit, or a wider network issue — the boiler's protection system will shut it down. Loose or corroded connections at the consumer unit, fused spur, or boiler wiring can also cause localised voltage drops that mimic a supply problem.
- Wiring faults or loose connections inside the boiler Common
Damaged cable insulation, loose terminal connections, or broken wires within the boiler's electrical harness can cause intermittent voltage drops that the PCB interprets as a supply fault. This is especially likely if the code appears sporadically rather than continuously.
- Incorrect polarity or inadequate electrical supply connection Sometimes
If the boiler was connected to an unsuitable spur, an extension lead, or a circuit with incorrect polarity, it may not receive a stable or correctly phased supply. This can cause the A34 code to appear from the moment of installation or after electrical work was carried out nearby.
- Faulty PCB (printed circuit board) Rare
A control board that has been repeatedly subjected to voltage surges or spikes can develop faults that cause it to misread the incoming supply voltage, triggering A34 erroneously even when the mains supply is fine. This is usually a diagnosis of exclusion — confirmed only after the supply and wiring have been ruled out.
How to fix it
- Check that your mains gas and electricity supplies are both on DIY safe
Confirm the boiler's fused spur switch is in the on position and that no circuit breakers in your consumer unit have tripped. If a breaker has tripped, reset it once — if it trips again immediately, do not continue and call an electrician.
- Check for any wider power supply issues in your home or street DIY safe
If other appliances are behaving unusually — lights dimming, appliances cutting out — the problem may be with the incoming supply from your energy network. Contact your electricity distribution network operator (DNO) if you suspect a street-level issue.
- Reset the boiler once or twice DIY safe
Locate the reset button on the control panel, usually marked with an 'R' or a flame symbol with a cross. Press and hold for one to two seconds. If the boiler fires up and runs normally, monitor it over the next hour. If A34 returns within a short period, do not keep resetting — a persistent fault requires an engineer.
- Do not attempt to inspect or adjust internal wiring or electrical components Gas Safe engineer
Checking terminal connections, replacing fuses within the boiler, or testing the PCB all require an engineer with the appropriate electrical and gas qualifications. Opening the boiler casing and working on live or recently live components carries a genuine risk of electric shock.
- Call a Gas Safe registered engineer to carry out a full electrical inspection Gas Safe engineer
A qualified engineer will use a multimeter to verify the incoming supply voltage, check wiring continuity, inspect all terminal connections, and confirm whether the PCB is reading voltage correctly. They will identify whether the fix is a straightforward rewire, a component replacement, or whether an electrician needs to address the supply side first.
- Have any faulty components replaced by the engineer Gas Safe engineer
Depending on findings, the engineer may replace damaged wiring, a voltage-sensitive sensor, or — as a last resort — the PCB itself. All of this work must be carried out by a competent person and, where it involves gas-side components, a Gas Safe registered engineer.
Parts you may need
- Ferroli PCB (control board) · from £180
- Boiler wiring loom / cable harness · from £45
- Fused spur isolator switch (external) · from £15
- Mains voltage surge protection device · from £30
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 A34 code dangerous — do I need to turn the boiler off immediately?
A34 is a protective lockout rather than an active safety emergency such as a gas leak. The boiler has already shut itself down. You do not need to isolate the gas supply, but you should leave the boiler off and not attempt to repeatedly reset it until the cause has been identified. If you smell gas at any point, leave the property, avoid operating switches, and call the National Gas Emergency Service on 0800 111 999.
Can a voltage issue like A34 damage my boiler's PCB over time?
Yes. Repeated exposure to voltage spikes or sustained low voltage can degrade the PCB gradually, even if the boiler appears to recover after each reset. If you live in an area prone to fluctuating supply voltage, an engineer may recommend fitting a voltage stabiliser or surge protection device on the boiler's circuit as a preventative measure.
How much does it typically cost to fix an A34 fault on a Ferroli boiler?
For most people, the repair involves an engineer call-out, a wiring inspection, and possibly a minor component fix — expect to pay roughly £100–£200 for that. If the PCB needs replacing, costs rise to around £250–£350 including parts and labour. A PCB alone for a Ferroli can cost upwards of £150–£200 for the part, plus an hour or two of labour. If your boiler is over ten years old and facing a PCB replacement, it is worth getting a new boiler quote at the same time.
My Ferroli shows A34 only in the morning — why would it be intermittent?
Mains voltage commonly drops during high-demand periods such as early morning when many households switch on kettles, showers, and heating simultaneously. If your boiler sits close to the lower end of its acceptable voltage range, it can trip on A34 during these peaks but recover once demand eases. An engineer can check your supply voltage across different times of day and advise whether a surge/stabilisation device or an electrical supply upgrade would resolve it.