A05 Boiler Fault Code: What It Means on Every Brand

The A05 fault code appears on 2 boiler brands — Andrews and Ferroli — and on all of them it points to the same kind of problem. The details still differ by brand (thresholds, sub-codes, reset procedure), so use the table below to jump to the page for your boiler.

Lockout — engineer likely 2 brands use this code

Which brand is your boiler?

The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.

Brand	What A05 means	Severity	DIY?
AAndrews	The A05 code indicates that the boiler or water heater has shut itself down because it cannot confirm the combustion fan is running correctly. Full guide →	Lockout — engineer likely	No
FFerroli	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… Full guide →	Lockout — engineer likely	No

A05 brand by brand

Andrews A05

The A05 code indicates that the boiler or water heater has shut itself down because it cannot confirm the combustion fan is running correctly. The fan is responsible for expelling harmful flue gases safely out of the appliance — without a confirmed fan signal, the unit will refuse to fire as a safety precaution. This lockout protects against dangerous gases building up inside the property. The fault may point to a failed fan motor, a wiring issue between the fan and the control board, a blocked flue or condensate pipe, a faulty air pressure switch, or in some cases a PCB fault mimicking fan failure.

Causes, fixes & costs for Andrews A05 → · All Andrews codes

Ferroli A05

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.

Causes, fixes & costs for Ferroli A05 → · All Ferroli codes

Frequently asked questions

Is the A05 fault code the same on every boiler?

Broadly, yes — on Andrews and Ferroli the A05 code points to the same class of fault, and the recommended response is similar. Model-specific details such as sub-codes and reset procedures still vary, so follow the page for your own brand.

Can I fix a A05 fault myself?

Not usually. On every brand listed, A05 points to a fault that needs a suitably registered engineer to diagnose and repair. A single reset to rule out a transient glitch is reasonable; repeated resets are not.

Who should I call about a A05 fault?

For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. If you smell gas at any point, leave the property and call the National Gas Emergency line on 0800 111 999.

General guidance only — not a substitute for professional advice, and not certified by a registered engineer. Any work on a gas appliance must be carried out by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.