A03 Boiler Fault Code: What It Means on Every Brand

The A03 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 A03 means	Severity	DIY?
AAndrews	The A03 fault code on Andrews boilers (including Andrews Water Heaters commercial units) signals a protective lockout, most commonly triggered by one of three underlying issues:… Full guide →	Lockout — engineer likely	No
FFerroli	The A03 code means your Ferroli boiler has detected that water temperature has risen beyond safe limits, most likely because water is not circulating properly around the system. Full guide →	Lockout — engineer likely	Some checks
VVokera	The A03 code appears when the boiler's printed circuit board (PCB) detects a problem with the fan's tacho signal — essentially, the feedback the PCB uses to confirm the fan is spinning at… Full guide →	Lockout — engineer likely	No

A03 brand by brand

Andrews A03

The A03 fault code on Andrews boilers (including Andrews Water Heaters commercial units) signals a protective lockout, most commonly triggered by one of three underlying issues: overtemperature protection activating when the flow temperature climbs too high, a fan fault where the flue-gas extraction fan is not running correctly, or in some model variants, an ignition failure. Because Andrews produces a range of commercial and domestic hot water appliances — many sharing control platforms with Ariston and Vokera-derived systems — the precise trigger can differ between models. In all cases the boiler or water heater shuts itself down as a safety measure. Do not attempt to override this lockout; the cause must be identified and corrected before normal operation can resume.

Causes, fixes & costs for Andrews A03 → · All Andrews codes

Ferroli A03

The A03 code means your Ferroli boiler has detected that water temperature has risen beyond safe limits, most likely because water is not circulating properly around the system. Unlike some advisory codes, A03 is a Type A lockout — the boiler shuts itself down completely and will not restart on its own. You must address the underlying cause before a manual reset will hold. The fault points primarily at the circulation pump or the sensor monitoring heat distribution, though air locks, low pressure, sludge, and wiring issues can all trigger the same code across Ferroli ranges including the Modena, Bluehelix, Optimax, and i-Series.

Causes, fixes & costs for Ferroli A03 → · All Ferroli codes

Vokera A03

The A03 code appears when the boiler's printed circuit board (PCB) detects a problem with the fan's tacho signal — essentially, the feedback the PCB uses to confirm the fan is spinning at the correct speed. Without a valid signal, the boiler cannot verify that exhaust gases are being safely expelled through the flue, so it locks out as a precaution. This fault is particularly prevalent on the Vokera Compact range but can appear across several Vokera models.

Causes, fixes & costs for Vokera A03 → · All Vokera codes

Frequently asked questions

Is the A03 fault code the same on every boiler?

Broadly, yes — on Andrews, Ferroli and Vokera the A03 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 A03 fault myself?

On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. The underlying repair usually needs a registered engineer. Never open the boiler casing yourself.

Who should I call about a A03 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.