Ferroli F15 Fault Code: Causes, Fixes & Repair Costs
What does the Ferroli F15 fault code mean?
The F15 code on a Ferroli boiler most commonly points to a fan-related problem — typically an interrupted tachometer signal, a wiring fault at the fan connection, a damaged fan motor, or debris obstructing the fan impeller. Because the fan is critical for safely venting combustion gases through the flue, the boiler locks out rather than risk unsafe operation. On some Ferroli model ranges (including certain i-Series and Optimax variants), F15 is instead associated with a flow sensor or temperature sensor fault, so it is worth checking your specific model's manual to confirm which definition applies. If you are unsure, treat the fault as requiring a Gas Safe engineer until confirmed otherwise.
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
- Interrupted or absent tachometer signal from the fan Common
The boiler's PCB monitors fan speed via a tachometer signal. If this signal is lost — due to a faulty fan motor, a broken or loose wiring connection at the fan, or the fan failing to spin at the correct speed — the boiler will not proceed to ignition and displays F15. This is the single most common root cause seen on Ferroli boilers displaying this code.
- Debris or obstruction in the fan Common
Insects, fluff, or material from a poorly maintained flue terminal can build up inside the fan housing, preventing the impeller from spinning freely. This can cause the tachometer signal to drop or become erratic, triggering the fault. A blocked or frozen flue outlet can have a similar effect by increasing back-pressure on the fan.
- PCB fault affecting fan control or signal interpretation Sometimes
If the PCB is not correctly sending the run signal to the fan, or is failing to read the returning tachometer signal, the boiler will fault even if the fan itself is perfectly healthy. PCB issues are more likely in older Ferroli units or those that have experienced a power surge.
- Flow sensor or temperature sensor fault (model-dependent) Sometimes
On certain Ferroli model ranges, F15 relates to a faulty or disconnected flow sensor or NTC temperature sensor rather than the fan. Symptoms here may differ slightly — for example the boiler might attempt to fire but shut down quickly. Check your boiler's manual to confirm whether this definition applies to your model.
- Damaged fan wiring loom Sometimes
Vibration over time can cause wiring insulation to crack or connectors to work loose between the fan and the PCB. A partial break in the wiring can cause an intermittent F15 that clears on reset but returns under load.
How to fix it
- Check the external flue terminal for obvious blockages DIY safe
Go outside and visually inspect the flue outlet (usually on an external wall or the roof). Look for bird nests, accumulated debris, ice, or snow blocking the terminal. Clear any external obstruction carefully if it is safe to do so. Do not attempt to access anything inside the boiler casing.
- Reset the boiler once or twice DIY safe
Most Ferroli boilers have a reset button on the control panel marked with an 'R' symbol. Press and hold it for one to two seconds. If the boiler fires up and runs normally, monitor it over the next hour. If F15 returns within a short period, do not keep resetting — repeated resets when a mechanical fault is present can cause heat exchanger damage. Two or three failed resets is your limit before calling an engineer.
- Have a Gas Safe engineer inspect and test the fan Gas Safe engineer
An engineer will remove the boiler casing and carry out electrical tests on the fan motor, checking that it spins freely, reaches the correct speed, and returns a clean tachometer signal to the PCB. They will also check the fan wiring harness and connectors for damage or loose terminals. If the fan is faulty, it will need to be replaced with a compatible Ferroli part.
- Have the engineer check the PCB and wiring loom Gas Safe engineer
If the fan tests as healthy, the engineer will use a multimeter to trace the tachometer signal circuit back to the PCB. A broken circuit can sometimes be repaired by rewiring a damaged section; if the PCB itself has failed, replacement will be required. On older or discontinued Ferroli models, confirm parts availability before committing to a PCB repair.
- Have the engineer inspect the flow or temperature sensor (if applicable to your model) Gas Safe engineer
If your Ferroli model's F15 definition relates to a sensor fault, the engineer will check the NTC thermistor or flow sensor resistance values with a multimeter and compare them to the manufacturer's specification. A sensor outside tolerance, or one with a loose or corroded connector, will need replacing.
- Call a Gas Safe registered engineer if the fault persists or you are unsure of the cause Gas Safe engineer
All internal boiler work — including fan replacement, PCB testing, sensor replacement, and wiring repairs — must be carried out by a Gas Safe registered engineer. You can verify any engineer's credentials at the Gas Safe Register website (gassaferegister.co.uk). Do not attempt to access internal gas or electrical components yourself.
Parts you may need
- Ferroli boiler fan / flue gas fan assembly · from £95
- Fan wiring harness / connector loom · from £25
- NTC temperature sensor (flow or return) · from £20
- Flow sensor · from £35
- PCB (printed circuit board) · 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 £150–£300, depending on the underlying cause.
Frequently asked questions
Is the Ferroli F15 code always a fan fault, or could it be something else?
F15 most commonly indicates a fan problem on Ferroli boilers — specifically issues with the fan motor, tachometer signal, wiring, or debris in the fan. However, on some Ferroli model ranges such as certain i-Series and Optimax variants, F15 can instead relate to a flow sensor or temperature sensor fault. The safest approach is to check your boiler's manual or data plate for the model number and cross-reference it against Ferroli's documentation, or ask your Gas Safe engineer to confirm before any parts are ordered.
Can I fix the Ferroli F15 fault myself?
The only DIY-safe steps are checking the external flue terminal for obvious blockages and performing one or two resets using the boiler's reset button. All internal work — including inspecting or replacing the fan, testing the PCB, or replacing sensors — requires a Gas Safe registered engineer. Opening the boiler casing and working near gas or live electrical components without the appropriate registration and training is unsafe and illegal.
How much does it typically cost to fix a Ferroli F15 fault in the UK?
Most people with an F15 fault pay somewhere between £150 and £300 all in, covering the engineer's callout, diagnosis, and the most common repair (fan or sensor replacement). A fan replacement including parts and labour typically runs £180–£250. A sensor replacement is usually cheaper at around £80–£120. PCB replacement is at the higher end, often £200–£300 for parts and labour. Note that on older or discontinued Ferroli models, parts can be harder to source, which may increase costs or lead times.
My Ferroli keeps showing F15 after I reset it — should I keep trying?
No. If F15 returns within a short time after resetting, limit yourself to two or three reset attempts in total. Repeatedly forcing the boiler to fire when a fan or sensor fault is present puts extra stress on the heat exchanger and other components, potentially turning a moderately priced fan repair into a much more expensive heat exchanger replacement. Call a Gas Safe engineer to diagnose the underlying cause.
How do I know if my Ferroli boiler is worth repairing or should be replaced?
A useful rule of thumb is to consider replacement if your boiler is over 10 years old and repair costs are approaching 30–40% of what a new boiler would cost. A straightforward fan or sensor repair on a Ferroli is usually cost-effective at any age. However, if the PCB has failed on an older out-of-warranty model, the combined cost of parts and labour can be high enough that a new, more efficient boiler is the better long-term investment. Your Gas Safe engineer can give you a balanced view once they have diagnosed the fault.