Ferroli Boiler Error Codes: Full Guide to Causes and Fixes 2026
Quick Answer: The most common Ferroli boiler error codes are F37 (low water pressure), F3/A03 (safety thermostat trip or heating sensor fault), and A01 (ignition failure). F37 is the only code most homeowners can resolve themselves by repressurising the system via the filling loop. All other Ferroli fault codes require a Gas Safe registered engineer to diagnose and repair. The D1 code, while not listed in official Ferroli documentation, is associated with a diverter valve fault and also requires an engineer.
Ferroli is an Italian boiler manufacturer with a presence in the UK budget and mid-range boiler market. Like all manufacturers, Ferroli uses a fault code system to communicate problems on the boiler’s control panel, and understanding what each code means is the fastest way to determine whether a quick DIY fix will restore heating and hot water or whether a Gas Safe engineer needs to be called. Ferroli boiler manuals can be downloaded directly from the Ferroli website if the original copy has been misplaced.
Ferroli Fault Code Prefixes: What A and F Codes Mean
Ferroli uses two main prefixes across their fault code range. A codes — such as A01, A06, and A09 — typically indicate active faults that have caused the boiler to lock out, usually related to ignition failures, flame loss, or gas valve problems. F codes — such as F37, F05, and F10 — indicate faults with specific components or system conditions such as pressure, sensors, and electrical supply. Both categories require the underlying cause to be resolved before the boiler will operate normally, and the vast majority require a Gas Safe engineer.
Common Ferroli Boiler Error Codes
F37 — Low Water Pressure
The F37 code is the most commonly seen Ferroli fault code and indicates that the system water pressure has dropped below the minimum level required for safe and effective boiler operation. It is the only Ferroli fault code that most homeowners can resolve themselves without calling a Gas Safe engineer.
The method for adding water to the system varies between Ferroli models — the filling loop may be a flexible braided hose with one or two valves, or a built-in lever depending on the specific boiler. The boiler manual confirms the exact method and the correct target pressure for the specific model. Adding water slowly while watching the pressure gauge and stopping at the recommended level will resolve the F37 in most cases. The boiler should restart normally once pressure is restored.
If the F37 code returns shortly after repressurising, a slow leak somewhere in the central heating system is the most likely cause. A Gas Safe engineer should locate and repair the source of the leak rather than the homeowner continuing to top up the pressure as an ongoing temporary measure.
Can you fix it yourself? Yes — repressurise via the filling loop to the manufacturer’s specified pressure. Call an engineer if pressure drops repeatedly.
F3 / A03 — Safety Thermostat Trip or Heating Sensor Fault
The F3 code indicates that the boiler’s safety thermostat has tripped, shutting the boiler down to prevent overheating damage. The A03 code indicates a fault with the heating sensor that can produce similar symptoms — either a damaged sensor, a lack of water circulating within the system, or air that has entered the heating circuit. All three causes produce conditions that prevent the boiler from accurately monitoring water temperature and result in a safety shutdown.
A lack of water circulation is most commonly caused by a failing pump or a closed or partially closed radiator valve. Air in the system can be identified by bleeding the radiators — if air escapes when a radiator bleed valve is opened, this confirms air is present in the circuit. However, identifying which of these causes is responsible for the F3 or A03 requires internal inspection of the boiler and heating system that must be carried out by a Gas Safe engineer.
Can you fix it yourself? No — a Gas Safe engineer is required to diagnose and repair the fault.
A01 — Ignition Failure
The A01 code means the boiler has attempted to ignite and failed, causing it to enter lockout mode. There are four possible causes — no gas reaching the burner, a faulty detection or ignition electrode, a damaged gas valve, or insufficient electrical power to initiate ignition. Of these, a gas supply interruption is the only one the homeowner can check independently. To address the issue, consulting a professional may be necessary as they can perform comprehensive keston boiler error code troubleshooting to pinpoint the exact problem. Ensuring that the gas supply is stable and conducting thorough checks on the electronic components can help in resolving the lockout situation. If the problem persists, contacting customer support for further guidance on advanced error codes is advisable.
Confirming that other gas appliances in the property — a gas hob, fire, or other boiler — are operating normally rules out a gas supply issue. If other appliances are working and the boiler is not, attempting a single reset is the next step. If A01 returns after one reset, a Gas Safe engineer should inspect the ignition electrode, gas valve, and electrical supply to the ignition system before the boiler is restarted.
Can you fix it yourself? Check the gas supply first and attempt one reset. Call a Gas Safe engineer if A01 persists.
D1 — Diverter Valve Fault
The D1 code does not appear in Ferroli’s official user guides, but is associated in practice with a diverter valve that is not opening fully, causing a restriction in the flow pipe. The diverter valve controls the direction of heated water between the central heating circuit and the domestic hot water circuit in a combi boiler, and a valve that is stuck or partially seized will cause flow problems that the boiler’s sensors detect as a fault.
Diverter valve inspection and replacement must be carried out by a Gas Safe engineer. It is worth noting the D1 code when calling an engineer as it helps direct the inspection to the valve and associated pipework.
Can you fix it yourself? No — a Gas Safe engineer should inspect the diverter valve.
Full Ferroli Boiler Error Code Reference
| Code | Fault | DIY Fix? |
|---|---|---|
| A01 | Ignition failure — faulty electrode or no gas | Check gas supply, attempt one reset, then engineer |
| A02 | Faulty electrode or card error | No — engineer required |
| A03 | Damaged heating sensor, lack of circulation, or air in system | No — engineer required |
| F04 | Incorrect card parameter setting | No — engineer required |
| F05 | Air pressure switch fault — flue baffle obstructed or incorrectly sized | No — engineer required |
| A06 | No flame after ignition — gas pressure issue | Check gas supply, attempt one reset, then engineer |
| F07 | Faulty air pressure switch — contacts closing when fan activates | No — engineer required |
| A09 | Faulty gas valve or wiring disconnection | No — engineer required |
| F10 | Faulty delivery sensor — short circuit or disconnection | No — engineer required |
| F11 | Faulty hot water sensor — damaged or disconnected | No — engineer required |
| A15 | F05 fault repeated multiple times in one day — faulty air pressure switch | No — engineer required |
| A16 | Faulty gas valve | No — engineer required |
| A23 | Card parameter fault — possible incorrect settings | No — engineer required |
| A24 | Card parameter fault — possible incorrect settings | No — engineer required |
| F34 | Electricity supply below 170V | Check consumer unit — contact electricity provider |
| F35 | Mains electricity frequency fault | No — contact electricity provider or engineer |
| F37 | Low water pressure or damaged pressure switch | Yes — repressurise via filling loop |
| F43 | Exchanger protection activation — lack of water or air in system | No — engineer required |
| F50 | Internal DBM23B controller error | No — engineer required |
| F51 | Internal DBM23B controller error | No — engineer required |
| D1 | Diverter valve not opening fully (not in official documentation) | No — engineer required |
Fault Code Detail: Key Secondary Codes
A02 — Faulty Electrode or Card Error
The A02 code indicates either a faulty ignition or detection electrode or an error with the boiler’s control card. A damaged electrode can prevent ignition or cause the boiler to fail to detect a flame correctly. A card error suggests a fault with the boiler’s electronic control board. Both require a Gas Safe engineer to diagnose and determine whether the electrode, the card, or both need replacement. In addition to these issues, understanding navien boiler error code solutions can be crucial for troubleshooting. Familiarizing yourself with common codes can help identify problems more quickly and streamline the repair process. Always consult a professional when dealing with electrical components for safety and reliability.
F04, A23, A24 — Card Parameter Faults
These codes all relate to the boiler’s control card parameters being set incorrectly or having developed a fault. They can appear after a power interruption, a failed component replacement, or a control board fault. An engineer with Ferroli product experience should access and correct the card settings or replace the card as required. In cases where the boiler continues to display issues, it is essential to explore ideal boiler error code solutions to identify underlying problems. Utilizing diagnostic tools and adhering to manufacturer guidelines can greatly assist in correcting these fault codes effectively. Prompt attention to the error codes will ensure the boiler operates efficiently and safely.
F05 and A15 — Air Pressure Switch and Flue Faults
The F05 code indicates a fault with the air pressure switch, which may also be triggered by a flue baffle that is obstructed or incorrectly sized for the installation. The A15 code appears when F05 has been triggered multiple times within a single day, indicating a persistent underlying problem rather than a one-off event. Both require a Gas Safe engineer to inspect the air pressure switch, flue system, and combustion air pathway before any components are replaced.
F07 — Air Pressure Switch Contacts Closing on Fan Activation
This specific variant of an air pressure switch fault occurs when the switch contacts close at the point the fan starts up rather than in response to correct air pressure. This indicates a faulty switch that is responding to fan vibration or electrical interference rather than actual pressure. Replacement by a Gas Safe engineer is required.
A06 — No Flame After Ignition Phase
Where A01 indicates the boiler failed to ignite at all, A06 indicates that ignition was initiated but no sustained flame was established immediately after. This points more specifically to a gas pressure issue preventing adequate fuel delivery after the ignition sequence begins, rather than an electrode or electrical fault. Confirming the gas supply is active and attempting one reset is appropriate before calling an engineer.
A09 and A16 — Gas Valve Faults
Both codes relate to the gas valve — A09 indicates the valve itself is faulty or that wiring to the valve has become disconnected, while A16 indicates a direct gas valve fault. The gas valve controls fuel delivery to the burner, and a valve that is not operating correctly is both an efficiency problem and a potential safety concern. Both codes require a Gas Safe engineer to inspect, test, and replace the valve as needed.
F10 and F11 — Delivery and Hot Water Sensor Faults
F10 indicates a fault with the heating delivery sensor — either a short circuit in the wiring or a disconnected sensor. F11 indicates a fault with the hot water sensor that has either been damaged or disconnected. Both are straightforward component replacement jobs for a Gas Safe engineer and are typically inexpensive repairs when the sensor itself is the only component that has failed.
F34 — Low Electrical Supply
The F34 code appears when the electrical supply to the boiler falls below 170V. This is not a boiler fault — it indicates a problem with the property’s mains electrical supply. Checking the consumer unit for tripped breakers is the first step, and if the issue persists, contacting the electricity network operator is the appropriate course of action. A Gas Safe engineer is only required if an internal wiring fault within the boiler is confirmed to be causing the low voltage reading.
F35 — Mains Electricity Frequency Fault
The F35 code indicates a problem with the frequency of the mains electricity supply to the boiler. As with F34, this is an electricity supply issue rather than a boiler fault and should be reported to the electricity network operator if it persists.
F43 — Heat Exchanger Protection Activation
The F43 code means the boiler’s heat exchanger protection system has intervened to prevent damage, most commonly triggered by a lack of water in the system or by air trapped within the circuit. Both conditions prevent adequate heat transfer through the heat exchanger and can cause it to overheat rapidly. A Gas Safe engineer should establish the underlying cause before the boiler is restarted, as repeated heat exchanger overheating is one of the most common causes of expensive early heat exchanger failure. An understanding of system boiler operation overview is crucial for both maintenance and troubleshooting. Regular checks and adherence to safety protocols can significantly extend the life of the boiler and enhance its efficiency. Additionally, it’s vital for homeowners to be informed about common boiler issues to prevent costly repairs and ensure optimal heating performance.
F50 and F51 — Internal Controller Errors
Both codes indicate internal errors within the DBM23B controller — the boiler’s main electronic control unit. These are electronic faults that require a Gas Safe engineer to diagnose at the component level, and may require controller replacement depending on the nature of the fault identified.
FAQ
What does the Ferroli F37 fault code mean?
The Ferroli F37 fault code indicates that the system water pressure has dropped below the minimum level required for safe boiler operation, or that the water pressure switch itself may be damaged. Low pressure is by far the most common cause. Repressurising the system via the filling loop — using the method described in the boiler manual for the specific Ferroli model — will resolve the fault in most cases. If F37 returns shortly after topping up, a water leak in the system is likely and a Gas Safe engineer should investigate the source.
Can I fix a Ferroli boiler fault myself?
F37 is the only Ferroli fault code that most homeowners can resolve themselves, by repressurising the system via the filling loop to the level specified in the boiler manual. For A01 and A06, confirming the gas supply is active and attempting a single reset is a reasonable first step before calling an engineer. The F34 code indicating low electrical supply can be investigated by checking the consumer unit. All other Ferroli fault codes require a Gas Safe registered engineer to diagnose and repair.
What is the Ferroli A01 fault code?
The Ferroli A01 fault code means the boiler has failed to ignite and has entered lockout mode. The four most common causes are no gas reaching the burner, a faulty detection or ignition electrode, a damaged gas valve, or insufficient electrical power for ignition. Checking that other gas appliances in the property are working confirms whether the gas supply is active. If the supply is fine and a single reset does not clear the fault, a Gas Safe engineer should inspect the ignition system before the boiler is restarted.
What does the Ferroli D1 code mean?
The Ferroli D1 code does not appear in official Ferroli user documentation but is associated in practice with a diverter valve that is not opening fully, causing a restriction in the flow pipe of a combi boiler. The diverter valve controls the routing of heated water between the heating circuit and the hot water circuit, and a partially seized valve will cause the flow problems that trigger the D1 display. A Gas Safe engineer should inspect and replace the diverter valve.
What is the difference between A codes and F codes on a Ferroli boiler?
On Ferroli boilers, A codes generally indicate active lockout faults — situations where the boiler has shut down and will not restart until the fault is resolved and a reset is performed. These typically relate to ignition failures, flame loss, and gas valve problems. F codes indicate component faults or system condition issues — such as pressure, sensor, and electrical faults — that may or may not cause a complete lockout depending on the severity. Both categories require the underlying cause to be identified before the boiler is returned to service, and the vast majority require a Gas Safe engineer. Ideal f1 fault code explained can help technicians understand the specific issues affecting the boiler’s operation. This code typically signifies a fault related to the airflow or combustion process, which must be diagnosed accurately to ensure proper functioning. Resolving the f1 fault often involves checking the fan, flue components, and overall ventilation to restore the system to normal operation.
How do I prevent Ferroli boiler fault codes?
Annual servicing by a Gas Safe registered engineer is the most effective way to prevent Ferroli fault codes from appearing. During a service the engineer cleans key components, checks gas pressure and combustion quality, inspects the flue, tests the air pressure switch and sensors, and identifies any components approaching the end of their service life. Many of the most common Ferroli codes — including A01, F05, F10, and F11 — are directly preventable through regular professional maintenance. Keeping the system pressure within the correct range also reduces the likelihood of F37 and F43 codes.
When should I replace a Ferroli boiler rather than repair it?
A Ferroli boiler under 10 years old with a single fault is almost always worth repairing. For boilers over 10 to 12 years old where multiple fault codes are recurring, where major components such as the control card, gas valve, or heat exchanger require replacement, or where repair costs are approaching 50% of a new boiler installation, replacement is likely the more economical long-term decision. A Gas Safe engineer can give an honest assessment of the boiler’s condition and advise on whether continued repair or replacement delivers better value for the specific situation.
Conclusion
Ferroli’s fault code system uses A and F prefixes to distinguish between active lockout faults and component or system condition issues, making it relatively straightforward to categorise the severity of a problem from the code alone. Of all the codes covered in this guide, only F37 can typically be resolved by the homeowner — by repressurising the system to the level specified in the boiler manual. Checking the gas supply before calling an engineer for A01 and A06 is also a practical first step that can occasionally save an unnecessary call-out.
For all other Ferroli fault codes, a Gas Safe registered engineer should be contacted promptly. Annual servicing remains the most effective prevention strategy, catching developing faults before they cause a lockout and keeping the boiler running at its rated efficiency throughout the 10 to 15-year operational lifespan that a well-maintained Ferroli boiler should achieve.
