Ferroli A05 Fault Code: Causes, Fixes & Repair Costs
What does the Ferroli A05 fault code mean?
The A05 code on a Ferroli boiler signals a problem with the flue exhaust fan — specifically, the boiler's control board has either lost the tachometer (speed sensor) signal from the fan for an hour or more, or is detecting no fan activity at all. Because the fan is critical for safely venting combustion gases out of your home, the boiler locks out completely when this signal is absent or interrupted. On the Ferroli Domiproject D/C range, A05 can also indicate that no fan connection is detected at all, pointing to a wiring or fan failure rather than just a speed-signal issue. As an 'A' code in Ferroli's fault system, this is a hard lockout — the boiler will not restart on its own and requires a manual reset before it will attempt to fire again.
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
- Fan motor failure or physical obstruction Common
The fan itself has seized, suffered bearing failure, or has debris lodged inside it preventing it from spinning at the correct speed. This stops the tachometer from generating a valid signal and is the most frequent root cause engineers find when attending an A05 fault.
- Tachometer signal wiring fault Common
The wiring between the fan's built-in speed sensor and the PCB has become loose, corroded, or broken. Even if the fan motor itself is working, the control board receives no confirmation that it is spinning, triggering the lockout.
- No 230V electrical supply reaching the fan Sometimes
A break in the wiring loom, a blown fuse on the PCB, or a loose connector can cut power to the fan entirely. The fan cannot spin without its supply voltage, so the boiler immediately detects a fault and locks out.
- PCB fault misreading the fan signal Rare
In rarer cases the fan and its wiring are both healthy but a failing PCB is unable to correctly interpret or receive the tachometer signal. This is usually identified by a Gas Safe engineer after all other causes have been ruled out.
How to fix it
- Reset the boiler once DIY safe
Locate the reset button on your Ferroli's control panel — it is usually marked with the letter 'R' or a circular arrow symbol. Press and hold it for one to two seconds. Allow the boiler a full minute to attempt a restart. If it fires up and runs normally, monitor it over the next hour or so to confirm the fault does not return.
- Check the flue outlet for obvious blockages DIY safe
Go outside and look at where your boiler's flue exits the building. After storms or periods of snowfall it is possible for debris, a bird's nest, or compacted snow to partially block the terminal. If you can safely see and reach the flue outlet and there is a clear obstruction, remove it carefully. Do not attempt to dismantle any internal flue components.
- Do not reset the boiler repeatedly DIY safe
If the A05 code returns after a single reset, stop resetting. Forcing the boiler to attempt ignition with a faulty fan risks driving exhaust gases into the appliance rather than out through the flue, and can cause expensive damage to the heat exchanger over time. Two resets maximum before calling a professional.
- Call a Gas Safe registered engineer to inspect the fan and wiring Gas Safe engineer
An engineer will open the boiler casing, verify that 230V is reaching the fan, test the tachometer signal with a meter, and physically inspect the fan for debris, damaged blades, or seized bearings. This is not work a homeowner should attempt — the fan is an internally mounted electrical and mechanical component inside a gas appliance.
- Engineer to replace the fan or repair the wiring loom if required Gas Safe engineer
If the fan motor has failed or the tachometer wiring is damaged, the engineer will source the correct replacement part for your Ferroli model and fit it. Once replaced, they will run the boiler through a full start-up sequence to confirm the fault has cleared and that flue gas readings are within safe limits.
- Engineer to test and replace the PCB if fan and wiring check out correctly Gas Safe engineer
Should the fan and all associated wiring prove healthy, the engineer will investigate the PCB as the likely source of the false or missing signal. PCB replacement requires safe isolation of the appliance and correct configuration of the replacement board for your specific boiler model.
Parts you may need
- Ferroli flue exhaust fan motor assembly · from £95
- Fan tachometer wiring harness/loom · from £25
- Ferroli PCB (control board) · from £140
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
Can I keep resetting my Ferroli boiler to clear the A05 code?
You should limit yourself to one, or at most two, manual resets. If the A05 code keeps coming back it means the underlying fault — most commonly a failed fan motor or a wiring problem — has not gone away. Repeatedly forcing a restart with a faulty fan is not safe and can put additional stress on the heat exchanger, potentially turning a £200 fan repair into a far more costly job.
Is the Ferroli A05 fault dangerous?
The boiler locks itself out as a precaution, so in that state it poses no immediate danger. The concern is that a fan which is not working correctly cannot reliably vent combustion gases outside. This is why the boiler refuses to fire without a functioning fan, and why you should not attempt to bypass or repeatedly override the lockout. Leave the boiler off and call a Gas Safe engineer promptly.
How much does it cost to fix a Ferroli A05 fault in the UK?
Most people with an A05 fault end up paying between £150 and £300 all in. A straightforward engineer visit to diagnose and reset, where the fan is simply obstructed by debris, sits at the lower end. A full fan motor replacement including parts and labour typically falls in the £180–£250 range. PCB replacement, if that turns out to be the root cause, generally costs £200–£300. If your boiler is over ten years old and repair costs are pushing toward 40% of a new boiler's price, it is worth getting a replacement quote at the same time.
What is the difference between an 'A' code and an 'F' code on a Ferroli boiler?
Ferroli uses two main categories of fault code. Codes beginning with 'F' are blocking faults — the boiler pauses until the triggering condition resolves itself and may then restart automatically. Codes beginning with 'A', like A05, are lockout faults — the boiler shuts down completely and will not attempt to restart until someone physically presses the reset button. Because A codes indicate the boiler has judged a condition serious enough to refuse automatic recovery, they always warrant investigation rather than repeated resets.