A24 Boiler Fault Code: What It Means on Every Brand

The A24 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 A24 means	Severity	DIY?
AAndrews	On the Andrews MAXXflo, fault codes are displayed as a letter followed by a number. Full guide →	Lockout — engineer likely	No
FFerroli	The A24 fault code on a Ferroli boiler indicates a card parameter error — meaning the boiler's control board (PCB) has detected a problem with its own internal settings or configuration. Full guide →	Lockout — engineer likely	No

A24 brand by brand

Andrews A24

On the Andrews MAXXflo, fault codes are displayed as a letter followed by a number. The letter indicates the fault type, and the number identifies which burner module is affected. The letter 'A' denotes a lockout fault — meaning the burner module has been shut down by the control system and cannot attempt to restart without a manual reset. The number '24' breaks down as follows: '2' identifies the fault type (gas valve relay error) and '4' identifies burner module 4 as the one that has locked out. In plain terms, the control system sent a command to open or close the gas valve relay on module 4 but received no confirmation that the relay responded correctly. As a safety measure, the system immediately locked that module out to prevent any unsafe condition. Note that the same relay fault occurring on other modules would appear as A21 (module 1), A22 (module 2), or A23 (module 3) — the diagnostic approach for each is identical, only the affected module differs.

Causes, fixes & costs for Andrews A24 → · All Andrews codes

Ferroli A24

The A24 fault code on a Ferroli boiler indicates a card parameter error — meaning the boiler's control board (PCB) has detected a problem with its own internal settings or configuration. In plain terms, the boiler's electronic brain has either lost its programmed parameters, encountered a configuration mismatch, or detected a hardware fault within the board itself. Because the PCB governs virtually every function of the boiler, this fault causes the boiler to lock out as a safety precaution. A24 is closely related to other PCB-type codes on Ferroli boilers — including A23, A26, F15, F20, F21, F40, F47, F50, F51, and F53 — all of which point to control board or parameter issues. Some sources also group A24 alongside F04 and F07 under the broader category of electronic board faults. Whatever the precise trigger, A24 almost always requires a Gas Safe engineer to investigate and resolve.

Causes, fixes & costs for Ferroli A24 → · All Ferroli codes

Frequently asked questions

Is the A24 fault code the same on every boiler?

Broadly, yes — on Andrews and Ferroli the A24 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 A24 fault myself?

Not usually. On every brand listed, A24 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 A24 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.