A09 Boiler Fault Code: What It Means on Every Brand

The A09 fault code appears on 3 boiler brands — Andrews, Ferroli and Vokera — 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 3 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 A09 means	Severity	DIY?
AAndrews	On Andrews water heaters and boilers, the letter 'A' in a fault code indicates a full lockout — the appliance has shut down completely and will not restart without a manual reset. Full guide →	Lockout — engineer likely	No
FFerroli	The A09 code on a Ferroli boiler is a lockout fault — meaning the boiler shuts down completely and requires a manual reset to restart. Full guide →	Lockout — engineer likely	No
VVokera	The A09 code on a Vokera boiler signals one of two things depending on the model and generation. Full guide →	Lockout — engineer likely	No

A09 brand by brand

Andrews A09

On Andrews water heaters and boilers, the letter 'A' in a fault code indicates a full lockout — the appliance has shut down completely and will not restart without a manual reset. A09 specifically points to a safety-critical issue with flame detection or gas valve integrity. In practical terms, this means the control system has detected a flame signal when no flame should be present (a 'false flame' condition), or has identified a problem with the gas valve failing to close fully, or — on certain models — a fault with the flue thermistor circuit. All three scenarios trigger an immediate lockout because they represent a potential safety hazard. Because Andrews appliances span several product families (MAXXflo, ECOflo, HIflo, COMBIflo and others), the precise meaning of A09 can vary slightly between control board variants, so always cross-reference with your model's data plate and service documentation.

Causes, fixes & costs for Andrews A09 → · All Andrews codes

Ferroli A09

The A09 code on a Ferroli boiler is a lockout fault — meaning the boiler shuts down completely and requires a manual reset to restart. Importantly, the exact meaning of A09 varies depending on which Ferroli model series you own. On the most widely used UK ranges — including the Modena, Optimax, Bluehelix, and i-Series — A09 points to a gas valve error, where the valve is failing to open or close as the boiler's control board expects. On certain older Ferroli models, A09 (sometimes paired with F09) instead indicates an overtemperature protection event, typically linked to a damaged return sensor, poor water circulation, or air trapped in the system. In both cases the boiler locks out as a safety precaution. Check your specific model's manual to confirm which meaning applies to your boiler, and always treat a lockout involving the gas valve as a job for a Gas Safe registered engineer.

Causes, fixes & costs for Ferroli A09 → · All Ferroli codes

Vokera A09

The A09 code on a Vokera boiler signals one of two things depending on the model and generation. Most commonly, it points to a fault with the flue thermistor — the sensor that monitors the temperature of exhaust gases leaving the boiler — or indicates that an internal condensing-hours counter has reached a threshold, telling you the boiler needs attention. On some Vokera models, A09 can alternatively mean the control board has detected a flame signal at a moment when no flame should be present (known as false flame detection), which may point to an electrical fault, a faulty flame sensor, or flue gas recirculation. In either case, the boiler will typically lock out to protect itself, and a reset alone may not resolve the underlying problem.

Causes, fixes & costs for Vokera A09 → · All Vokera codes

Frequently asked questions

Is the A09 fault code the same on every boiler?

Broadly, yes — on Andrews, Ferroli and Vokera the A09 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 A09 fault myself?

Not usually. On every brand listed, A09 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 A09 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.