723 Boiler Fault Code: What It Means on Every Brand

The 723 fault code appears on 2 boiler brands — Ariston and Chaffoteaux — 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 723 means	Severity	DIY?
AAriston	Fault code 723 indicates that the boiler has detected an overheat condition in heating Zone 3. Full guide →	Lockout — engineer likely	No
CChaffoteaux	Fault code 723 on a Chaffoteaux boiler indicates that an overtemperature condition has been detected in Zone 3 of the heating system. Full guide →	Lockout — engineer likely	No

723 brand by brand

Ariston 723

Fault code 723 indicates that the boiler has detected an overheat condition in heating Zone 3. The system's temperature sensor has registered temperatures beyond safe operating limits in that zone, causing the boiler to lock out automatically as a protective measure. This code appears on Ariston Clas Net One, Clas One, E-Combi, and E-System models — it is the Zone 3 equivalent of code 707 (which performs the same function on E-Combi Evo and Clas HE Evo models). If you see 723 on your display, the boiler will not restart normally until the underlying cause is identified and resolved. Do not repeatedly reset without investigating, as continued overheating can damage internal components.

Causes, fixes & costs for Ariston 723 → · All Ariston codes

Chaffoteaux 723

Fault code 723 on a Chaffoteaux boiler indicates that an overtemperature condition has been detected in Zone 3 of the heating system. Chaffoteaux uses a structured numbering system for its fault codes: the leading digit (7) identifies the multizone hydraulic circuit group, while the trailing digits (23) pinpoint Zone 3 specifically. In plain terms, the boiler's control electronics have registered that water temperature in Zone 3 has exceeded safe limits, and the boiler has locked out as a safety precaution. This code appears on multizone-capable Chaffoteaux models such as those in the Mira Advance and Pigma Green ranges. If left unaddressed, repeated overtemperature events can cause premature wear to components, so it is important to identify the root cause rather than simply resetting the boiler repeatedly.

Causes, fixes & costs for Chaffoteaux 723 → · All Chaffoteaux codes

Frequently asked questions

Is the 723 fault code the same on every boiler?

Broadly, yes — on Ariston and Chaffoteaux the 723 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 723 fault myself?

Not usually. On every brand listed, 723 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 723 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.