601 Boiler Fault Code: What It Means on Every Brand

The 601 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 601 means	Severity	DIY?
AAriston	Ariston fault code 601 sits within the 600-series, which covers flue, fan, and air pressure switch issues — all safety-critical systems that ensure combustion gases leave your home safely. Full guide →	Lockout — engineer likely	No
CChaffoteaux	Fault code 601 on a Chaffoteaux boiler indicates that the boiler's safety system has detected a problem with exhaust gas evacuation. Full guide →	Lockout — engineer likely	No

601 brand by brand

Ariston 601

Ariston fault code 601 sits within the 600-series, which covers flue, fan, and air pressure switch issues — all safety-critical systems that ensure combustion gases leave your home safely. The code has two main interpretations depending on your specific Ariston model. On open-flue (atmospheric) models, it signals that the flue gas overheat sensor has tripped, meaning exhaust gases have reached a temperature beyond safe limits. On room-sealed (fan-assisted) models, the same code can indicate a fan speed or tachometer fault, where the boiler's PCB has detected that the fan is not spinning at the correct speed — or not spinning at all. In either case, the boiler will lock out and refuse to fire until the underlying problem is resolved. Do not continue using the boiler until a Gas Safe registered engineer has assessed it, as both fault types carry a risk of harmful gases not being properly expelled.

Causes, fixes & costs for Ariston 601 → · All Ariston codes

Chaffoteaux 601

Fault code 601 on a Chaffoteaux boiler indicates that the boiler's safety system has detected a problem with exhaust gas evacuation. The boiler monitors this via a flue gas sensor or air pressure switch — a safety device that confirms combustion gases are being properly expelled through the flue before allowing ignition. When this sensor fails to detect normal draught conditions, the boiler enters a safety lockout to prevent the risk of harmful gases — including carbon monoxide — entering your home. The boiler will attempt to restart after approximately 12 minutes; if conditions return to normal it may fire successfully, but if the fault persists it will lock out again. Because this fault directly involves flue gas safety, a Gas Safe registered engineer should be involved in diagnosis and repair.

Causes, fixes & costs for Chaffoteaux 601 → · All Chaffoteaux codes

Frequently asked questions

Is the 601 fault code the same on every boiler?

Broadly, yes — on Ariston and Chaffoteaux the 601 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 601 fault myself?

Not usually. On every brand listed, 601 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 601 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.