Ferroli A09 Fault Code: Causes, Fixes & Repair Costs
What does the Ferroli A09 fault code mean?
The A09 code on a Ferroli boiler is a lockout fault — meaning the boiler shuts down completely and requires a manual reset to restart. Importantly, the exact meaning of A09 varies depending on which Ferroli model series you own. On the most widely used UK ranges — including the Modena, Optimax, Bluehelix, and i-Series — A09 points to a gas valve error, where the valve is failing to open or close as the boiler's control board expects. On certain older Ferroli models, A09 (sometimes paired with F09) instead indicates an overtemperature protection event, typically linked to a damaged return sensor, poor water circulation, or air trapped in the system. In both cases the boiler locks out as a safety precaution. Check your specific model's manual to confirm which meaning applies to your boiler, and always treat a lockout involving the gas valve as a job for a Gas Safe registered engineer.
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
- Gas valve wiring fault or loose connection Common
The most frequent trigger on Modena, Optimax, Bluehelix, and i-Series boilers. Vibration over time can loosen the electrical connector at the gas valve, or wiring insulation can degrade. The PCB detects that the valve is not responding as commanded and immediately locks the boiler out to prevent an unsafe condition.
- Faulty or seized gas valve Common
The gas valve itself can fail mechanically or electrically — internal solenoids wear out, the valve can stick open or closed, or the coil resistance drifts outside acceptable limits. A Gas Safe engineer will test the valve electrically before condemning it, as replacement is required if it fails testing.
- Inadequate mains voltage supply to the valve Sometimes
Gas valves require a stable voltage to operate their solenoids correctly. If the mains supply to the boiler is fluctuating or consistently low, the valve may not actuate reliably, triggering A09 even though the valve itself is in good condition.
- Damaged return sensor or overtemperature event (older models only) Sometimes
On older Ferroli ranges where A09 refers to overtemperature protection, the return thermistor may have failed or drifted out of calibration, causing the PCB to believe water is returning at a dangerously high temperature. Trapped air or poor system circulation can also cause genuine overtemperature events that trigger this lockout.
- PCB fault misreporting the gas valve Rare
In rare cases the control board itself develops a fault and incorrectly reports a gas valve error. This is usually only confirmed after a Gas Safe engineer has tested and cleared the gas valve and wiring as potential causes.
How to fix it
- Check that your gas supply is working DIY safe
Before anything else, check that other gas appliances in your home — such as a gas hob or gas fire — are working normally. If nothing gas-powered is working, call your gas supplier or the National Gas Emergency Service on 0800 111 999. If your gas supply is fine, move to the next step.
- Attempt a single manual reset of the boiler DIY safe
Most Ferroli boilers have a reset button marked with 'R' or a flame symbol. Press and hold it for around 5 to 10 seconds until the boiler attempts to restart. If the boiler fires up and runs normally, monitor it closely over the next hour. If the A09 code returns within a short time, do not keep resetting — repeated resets on a genuine gas valve fault can cause expensive secondary damage. Limit yourself to two or three reset attempts total.
- Check system pressure (if your model also shows overtemperature symptoms) DIY safe
If your boiler is an older model where A09 relates to overtemperature or poor circulation, check the pressure gauge on the boiler front panel. It should read between 1.0 and 1.5 bar when the system is cold. If it reads below 1.0 bar, top up using the filling loop — consult your boiler's user guide for the location of the filling loop on your specific model.
- Do not attempt to inspect or work on the gas valve or wiring Gas Safe engineer
The gas valve is a gas-carrying component and must only be worked on by a Gas Safe registered engineer. Do not remove the boiler casing, touch any wiring connected to the valve, or attempt to bypass or manually operate the valve. This applies regardless of whether you believe the fault is wiring-related or mechanical.
- Call a Gas Safe registered engineer to diagnose and repair the fault Gas Safe engineer
A qualified engineer will inspect the wiring harness and connectors at the gas valve, test the valve electrically (checking solenoid resistance and operation), verify the mains voltage supply to the appliance, and test the return sensor if your model uses A09 for the overtemperature meaning. They will replace whichever component has failed — whether that is the gas valve, the return thermistor, or in rare cases the PCB. Always verify an engineer's Gas Safe registration before work begins at www.gassaferegister.co.uk and ask to see their Gas Safe ID card.
Parts you may need
- Ferroli gas valve · from £130
- Gas valve wiring harness / connector · from £25
- Return temperature thermistor (NTC sensor) · from £20
- Boiler control PCB (if required) · from £180
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–£350, depending on the underlying cause.
Frequently asked questions
Is the A09 code always a gas valve fault on every Ferroli boiler?
No — and this is worth checking carefully. On popular UK Ferroli ranges such as the Modena, Optimax, Bluehelix, and i-Series, A09 is documented as a gas valve error. However, on certain older Ferroli models the same A09 code (sometimes displayed alongside F09) indicates an overtemperature protection event caused by a damaged return sensor, trapped air, or poor water circulation. Look up your specific model number in the manufacturer's manual or contact Ferroli UK to confirm which meaning applies before assuming either cause.
Can I reset a Ferroli A09 fault myself?
You can attempt a reset — press and hold the reset button (marked 'R' or with a flame symbol) for around 5 to 10 seconds. If the boiler restarts and runs normally, monitor it over the next hour. However, if the A09 code returns after one or two resets, stop resetting and call a Gas Safe engineer. Repeatedly forcing a boiler to restart when there is a genuine gas valve fault risks damaging the heat exchanger and other components, turning a £250 repair into a much more expensive one.
How much does it cost to fix a Ferroli A09 fault in the UK?
For most people, repair costs fall between £100 and £350. A diagnostic visit and reset by a Gas Safe engineer typically costs £80 to £150. If the return sensor needs replacing, expect to pay roughly £80 to £150 all in. A gas valve replacement — the most common repair for this code — usually runs £250 to £350 including parts and labour. In rare cases where the PCB is at fault, costs can rise to £350 to £500 or more. If your Ferroli is over 10 years old and repair costs are approaching £500 or beyond, it is worth getting a replacement boiler quote to compare.
Is it safe to keep using my boiler while showing the A09 code?
No. A09 is a lockout code, which means the boiler has already shut itself down and will not fire until it is reset. This is a deliberate safety measure by the boiler's control system. You should not attempt to keep the boiler running by repeatedly resetting it — particularly if A09 relates to the gas valve, as an unsafe gas valve condition is exactly the kind of hazard the lockout is designed to prevent. Call a Gas Safe engineer promptly. If at any point you smell gas, leave the property immediately and call the National Gas Emergency Service on 0800 111 999.