110 Boiler Fault Code: What It Means on Every Brand

The 110 fault code appears on 3 boiler brands — Ariston, ATAG 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 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 110 means	Severity	DIY?
AAriston	Fault code 110 on Ariston boilers indicates that the central heating flow temperature probe has developed an open or short circuit. Full guide →	Lockout — engineer likely	No
AATAG	Fault code 110 on an ATAG boiler indicates that the appliance has detected an unsafe condition — either the water temperature has climbed beyond its safe upper limit (an overheat lockout),… Full guide →	Lockout — engineer likely	No
CChaffoteaux	Fault code 110 (displayed as '1 10' on some models) indicates that the boiler's flow temperature probe — an NTC thermistor that continuously measures the temperature of water leaving the… Full guide →	Lockout — engineer likely	No

110 brand by brand

Ariston 110

Fault code 110 on Ariston boilers indicates that the central heating flow temperature probe has developed an open or short circuit. This probe, known as an NTC thermistor, sits on the heating flow pipe and continuously feeds water temperature readings to the boiler's PCB. When the PCB loses a reliable signal — either because resistance has gone out of range (open circuit) or has dropped to near zero (short circuit) — it cannot safely control the burner, so the boiler locks out as a precaution. The fault applies across the full range of Ariston boiler models and will typically stop both heating and hot water until it is resolved.

Causes, fixes & costs for Ariston 110 → · All Ariston codes

ATAG 110

Fault code 110 on an ATAG boiler indicates that the appliance has detected an unsafe condition — either the water temperature has climbed beyond its safe upper limit (an overheat lockout), or system water pressure has risen to a dangerously high level. In either scenario the boiler shuts itself down as a protective measure. The overheating interpretation is the more widely referenced meaning, and ATAG's own fault-finding guidance notes that a very rapid rise in flow temperature — sometimes as much as 7–15 °C within a single second — can point to a sudden loss of water flow across the heat exchanger. Left unaddressed, repeated overheat events can cause secondary damage to components such as the pump, thermistor, or even the PCB, so prompt investigation is important.

Causes, fixes & costs for ATAG 110 → · All ATAG codes

Chaffoteaux 110

Fault code 110 (displayed as '1 10' on some models) indicates that the boiler's flow temperature probe — an NTC thermistor that continuously measures the temperature of water leaving the heat exchanger — has been detected as damaged or has failed entirely. Because the boiler relies on this sensor to monitor water temperature and prevent overheating, it cannot operate safely without a reliable reading and will lock out until the issue is resolved. This is a sensor fault, not simply an overheating event; do not confuse it with code 101 (overheat lockout), though the two are related. Note that fault code numbering varies across Chaffoteaux ranges: the '1 10' designation is confirmed for the Expert Control range. If your model is a Pigma, Britony, Urbia, or an older variant, verify the code against your own manual or call a Gas Safe engineer with your exact model name and code.

Causes, fixes & costs for Chaffoteaux 110 → · All Chaffoteaux codes

Frequently asked questions

Is the 110 fault code the same on every boiler?

Broadly, yes — on Ariston, ATAG and Chaffoteaux the 110 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 110 fault myself?

Not usually. On every brand listed, 110 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 110 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.