112 Boiler Fault Code: What It Means on Every Brand

The 112 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 112 means	Severity	DIY?
AAriston	Fault code 112 appears on Ariston boilers when the control board detects a problem with the central heating return temperature probe circuit. Full guide →	Lockout — engineer likely	No
AATAG	Fault code 112 on an Atag boiler indicates a problem with the return temperature sensor, also known as the T2 or NTC probe. Full guide →	Engineer may be needed	No
CChaffoteaux	Fault code 112 on a Chaffoteaux boiler indicates that the PCB has detected a problem with the NTC thermistor monitoring the water temperature at the inlet of the main heat exchanger. Full guide →	Lockout — engineer likely	No

112 brand by brand

Ariston 112

Fault code 112 appears on Ariston boilers when the control board detects a problem with the central heating return temperature probe circuit. This means the sensor fitted to the return pipe — the pipe that carries cooled water back into the boiler — is either reading an open circuit (broken connection) or a short circuit (unintended electrical contact). Because the boiler relies on this sensor to monitor water temperature accurately and operate safely, it locks out immediately when the signal is lost or unreliable. The probe itself is a small thermistor: a component whose electrical resistance changes in proportion to temperature, constantly feeding data to the PCB. When that data stream becomes erratic or disappears entirely, the boiler shuts down rather than risk overheating or damage.

Causes, fixes & costs for Ariston 112 → · All Ariston codes

ATAG 112

Fault code 112 on an Atag boiler indicates a problem with the return temperature sensor, also known as the T2 or NTC probe. This sensor sits on the return pipework and continuously monitors the temperature of the water coming back into the boiler from the central heating circuit. It works by changing its electrical resistance as temperature rises or falls, feeding that information to the PCB so the boiler can regulate itself correctly. When code 112 appears, the PCB has detected that the T2 sensor is reporting a value outside the expected range — or no signal at all — suggesting the probe itself, its wiring, or the PCB connection may be at fault.

Causes, fixes & costs for ATAG 112 → · All ATAG codes

Chaffoteaux 112

Fault code 112 on a Chaffoteaux boiler indicates that the PCB has detected a problem with the NTC thermistor monitoring the water temperature at the inlet of the main heat exchanger. The boiler's control board is receiving either no signal at all (open circuit) or a garbled, out-of-range signal (short circuit) from this sensor, so it shuts down as a precaution to prevent overheating or unsafe operation. In plain terms, the boiler can no longer trust the temperature reading at the point where water enters the heat exchanger, and it will not fire until the issue is resolved.

Causes, fixes & costs for Chaffoteaux 112 → · All Chaffoteaux codes

Frequently asked questions

Is the 112 fault code the same on every boiler?

No. 112 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 112 fault myself?

Not usually. On every brand listed, 112 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 112 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.