103 Boiler Fault Code: What It Means on Every Brand

The 103 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 103 means	Severity	DIY?
AAriston	Ariston fault code 103 signals that the boiler has detected insufficient water circulation through the heating system. Full guide →	Lockout — engineer likely	No
CChaffoteaux	Fault code 103 on a Chaffoteaux boiler indicates that the appliance has detected a problem with water circulation in the heating circuit — sometimes described internally as a 'flow check… Full guide →	Lockout — engineer likely	No

103 brand by brand

Ariston 103

Ariston fault code 103 signals that the boiler has detected insufficient water circulation through the heating system. Specifically, the flow temperature is climbing too rapidly — faster than 7°C per second — which tells the boiler's safety logic that not enough water is moving around the circuit to carry heat away safely. Without adequate flow, the heat exchanger risks overheating and sustaining permanent damage, so the boiler locks out to protect itself. This fault is closely related to codes 104–107, which all fall under the same 'insufficient circulation' family on Ariston boilers; code 103 is the most frequently seen of the group and is typically the starting point for diagnosis. The fault appears across the full range of Ariston combi and system boilers, including the E-Combi, E-System, Clas, and Genus ranges.

Causes, fixes & costs for Ariston 103 → · All Ariston codes

Chaffoteaux 103

Fault code 103 on a Chaffoteaux boiler indicates that the appliance has detected a problem with water circulation in the heating circuit — sometimes described internally as a 'flow check failed' condition. When the boiler cannot confirm that water is moving through the system at an adequate rate, it shuts itself down as a safety precaution to prevent overheating and damage to internal components. You may notice the boiler locking out, cold radiators, gurgling or banging noises from the pipework, or a pressure gauge reading that is lower than normal. On some Chaffoteaux models the code 103 appears alongside code 1P1, both pointing to the same underlying circulation anomaly.

Causes, fixes & costs for Chaffoteaux 103 → · All Chaffoteaux codes

Frequently asked questions

Is the 103 fault code the same on every boiler?

Broadly, yes — on Ariston and Chaffoteaux the 103 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 103 fault myself?

Not usually. On every brand listed, 103 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 103 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.