A15 Boiler Fault Code: What It Means on Every Brand

The A15 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 A15 means	Severity	DIY?
AAndrews	On Andrews commercial water heaters and boilers (including the MAXXflo and CWH range), fault codes beginning with the letter 'A' indicate a lockout condition — the appliance has shut… Full guide →	Lockout — engineer likely	No
FFerroli	The A15 code is a manual-reset lockout that appears when your Ferroli boiler has triggered the F05 blocking fault five times within a single 24-hour period. Full guide →	Lockout — engineer likely	No

A15 brand by brand

Andrews A15

On Andrews commercial water heaters and boilers (including the MAXXflo and CWH range), fault codes beginning with the letter 'A' indicate a lockout condition — the appliance has shut itself down as a safety precaution and will not restart without investigation and a manual reset. Code A15 specifically points to the air pressure switch failing to confirm that the fan is running correctly within the expected timeframe (typically around 20 seconds after fan start). The air pressure switch is a critical safety device: it monitors whether the fan is generating sufficient draught to safely expel combustion gases through the flue. If the switch does not detect the expected pressure differential — for any reason — the appliance locks out rather than risk firing without proper ventilation. Note that Andrews appliances cover several product families (MAXXflo, CWH, ClassicFlo, ECOflo); while A15 most commonly relates to the air pressure switch circuit on MAXXflo and CWH series units, always cross-reference with your specific model's technical manual or contact Andrews' technical helpline (part of Baxi Heating UK) to confirm the code definition for your exact appliance.

Causes, fixes & costs for Andrews A15 → · All Andrews codes

Ferroli A15

The A15 code is a manual-reset lockout that appears when your Ferroli boiler has triggered the F05 blocking fault five times within a single 24-hour period. The F05 fault itself relates to the air pressure switch, a safety device that confirms the fan is generating sufficient draught to safely expel combustion gases through the flue. When that switch fails to register the correct pressure reading repeatedly throughout the day, the boiler escalates the situation to a full A15 lockout rather than continuing to attempt automatic recovery. Because this code represents a pattern of failures rather than a single one-off event, it almost always points to an underlying mechanical or component problem that needs a Gas Safe engineer to diagnose properly.

Causes, fixes & costs for Ferroli A15 → · All Ferroli codes

Frequently asked questions

Is the A15 fault code the same on every boiler?

Broadly, yes — on Andrews and Ferroli the A15 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 A15 fault myself?

Not usually. On every brand listed, A15 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 A15 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.