111 Boiler Fault Code: What It Means on Every Brand

The 111 fault code appears on 3 brands — Ariston, ATAG and Chaffoteaux — and it does not mean the same thing on each. The same two or three characters can signal a pressure problem on one boiler and an ignition fault on another, so identify your brand first and use the table below to jump to the right page.

Up to: Lockout — engineer likely 3 brands use this code Meaning differs by brand

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 111 means	Severity	DIY?
AAriston	Fault code 111 signals that your Ariston boiler has detected water pressure in the heating system has dropped below the minimum safe operating level. Full guide →	Engineer may be needed	Some checks
AATAG	ATAG fault code 111 indicates that the boiler has detected a water temperature above its maximum permitted threshold and has locked out as a safety precaution. Full guide →	Lockout — engineer likely	No
CChaffoteaux	Fault code 111 on most Chaffoteaux boilers indicates that the flow temperature has climbed to or beyond the maximum safe threshold, causing the boiler to lock itself out as a protective… Full guide →	Lockout — engineer likely	No

111 brand by brand

Ariston 111

Fault code 111 signals that your Ariston boiler has detected water pressure in the heating system has dropped below the minimum safe operating level. What makes this code distinct from the similar code 108 is that it applies specifically to Ariston models equipped with an automatic filling (auto-replenishment) system. In theory, these boilers can top themselves up without any manual intervention — so when code 111 appears, it means the auto-fill mechanism has either attempted to restore pressure and failed, or cannot raise pressure to the required level at all. Most Ariston boilers need a cold system pressure of between 1.0 and 1.5 bar; a reading below 1.0 bar will typically trigger this fault. The underlying problem may be a leak somewhere in the system, a fault with the auto-fill device itself, or pressure lost gradually over time.

Causes, fixes & costs for Ariston 111 → · All Ariston codes

ATAG 111

ATAG fault code 111 indicates that the boiler has detected a water temperature above its maximum permitted threshold and has locked out as a safety precaution. The boiler will not restart until the underlying cause has been identified and resolved. In some ATAG models or third-party references the same code is also linked to ignition failure, so if a reset does not clear the fault a Gas Safe engineer should confirm the exact trigger on your specific appliance.

Causes, fixes & costs for ATAG 111 → · All ATAG codes

Chaffoteaux 111

Fault code 111 on most Chaffoteaux boilers indicates that the flow temperature has climbed to or beyond the maximum safe threshold, causing the boiler to lock itself out as a protective measure. The overheating thermostat — mounted on the outlet pipe of the primary heat exchanger — has triggered a shutdown to prevent damage. On Expert Control models, the code appears as '1 11' in the error table (group 1, fault 11), covering overheating and flow-check failures. On Ariston-platform Chaffoteaux models (which share control architecture with Ariston Thermo Group boilers), 111 sits alongside codes 108 and 112 which relate to automatic replenishment and return-pipe sensor faults respectively. On Pigma NOx and similar ranges the same overheating pattern presents under this code family. Important note: older Chaffoteaux models without a screen communicate faults through numbered LED flash sequences rather than a numeric display, so always cross-reference your model's manual to confirm the meaning before acting.

Causes, fixes & costs for Chaffoteaux 111 → · All Chaffoteaux codes

Frequently asked questions

Is the 111 fault code the same on every boiler?

No. 111 means different things on different brands — see the table above. Always identify your boiler's brand (it is printed on the front casing) before acting on any advice about the code.

Can I fix a 111 fault myself?

On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. Where the code is a simple pressure or reset condition, that may be all it needs. Never open the boiler casing yourself.

Who should I call about a 111 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.