Ferroli A05 fault codewhat it means and how to fix it
The fan tachometer signal has been missing for an hour or more. The appliance has stopped and needs an engineer.
Take care
Get a Gas Safe registered engineer to look at your Ferroli A05
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
What A05 means
A05 is the Ferroli fan fault on the Optimax and T-One ranges, and the manual defines it precisely: "fan problem — tachometer signal interrupted for 1 hour or longer". That one-hour qualifier is the interesting part, because F15 in the same table is also "fan problem", with the tachometer signal interrupted but no duration attached.
The natural reading, and the one engineers work to, is that a brief interruption shows as an F15 that clears itself while an interruption lasting an hour becomes the permanent A05 — so an appliance that has been throwing an intermittent F15 and has now locked out on A05 has not developed a new fault.
Ferroli do not actually spell that escalation out, unlike the A04 one where they name the trigger, so treat it as the sensible inference it is rather than as their statement. The fan proves that combustion products can be cleared through the flue, and no condensing appliance will open its gas valve without that proof. Ferroli direct a check of the wiring as well as the fan itself, and that ordering is sensible: a tachometer signal can be lost to a corroded connector while the fan spins perfectly well.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Fan bearings worn | The dominant cause beyond about eight years of service, and usually preceded by months of grumbling on start-up. | Common |
| Wiring or connector fault losing the tachometer signal | Ferroli list checking the wiring before the fan. The fan may be turning normally while the board hears nothing from it. | Occasional |
| Flue obstructed | A nest or debris in the terminal changes the load on the fan and therefore its speed, throwing the check even on a healthy fan. | Occasional |
| Control board input fault | The board cannot read a good signal. Considered only once the fan and its wiring have been eliminated. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£180–£420
A fan assembly is typically £280 to £420 fitted. A wiring repair or flue clearance is a call-out charge of £80 to £140.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
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Related Ferroli fault codes
- F07Get it checkedFlue gas temperature has stayed above 95°C for more than two minutes. Three of these in a day becomes a permanent A04 lockout.Related: fan and flue
- A01Get it checkedThe burner failed to light and the appliance has locked out. Ferroli list a blocked siphon as a cause, which is worth checking early.Related: same brand
- F37Usually simple to fixSystem water pressure is outside the correct range. Because this is an F code it clears by itself once you top the system back up.Related: same brand
- A03Get it checkedHigh limit protection has operated. Ferroli point at circulation and at the flow sensor position, and both are worth checking.Related: same brand
- A02Stop — call an engineerA flame is being detected while the burner should be off. Switch the appliance off and get a Gas Safe engineer to it.Related: same brand
Own a Ferroli boiler? Save it and its codes come first next time.
Related guides
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.