612 Boiler Fault Code: What It Means on Every Brand

The 612 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 612 means	Severity	DIY?
AAriston	Fault code 612 on Ariston boilers signals a fan fault that has escalated beyond the initial warning stage. Full guide →	Lockout — engineer likely	No
AATAG	Fault code 612 on Atag boilers (including the iC, iS, and iR ranges) indicates that the boiler's fan has failed to start up when commanded to do so. Full guide →	Lockout — engineer likely	No
CChaffoteaux	Fault code 612 on a Chaffoteaux boiler indicates that the boiler's control system has detected a problem with the flue extraction fan. Full guide →	Lockout — engineer likely	No

612 brand by brand

Ariston 612

Fault code 612 on Ariston boilers signals a fan fault that has escalated beyond the initial warning stage. The '6' prefix indicates a problem with air movement — either the intake of fresh air or the expulsion of flue gases. Typically, Ariston boilers first display code 611 as an early warning of an air or flue issue; if that underlying problem goes unresolved, the boiler escalates to 612 and locks out. At this point the boiler's control board has detected that the fan is not performing as expected and has shut the appliance down as a safety measure, since combustion products cannot be safely exhausted without a working fan.

Causes, fixes & costs for Ariston 612 → · All Ariston codes

ATAG 612

Fault code 612 on Atag boilers (including the iC, iS, and iR ranges) indicates that the boiler's fan has failed to start up when commanded to do so. The fan is a critical safety component: it draws combustion gases through the heat exchanger and expels them safely via the flue. Without confirmation that the fan is running correctly, the boiler's control board will prevent ignition entirely — so the boiler will not fire until the fault is resolved. In most cases the display will show '612' alongside a fan fault message.

Causes, fixes & costs for ATAG 612 → · All ATAG codes

Chaffoteaux 612

Fault code 612 on a Chaffoteaux boiler indicates that the boiler's control system has detected a problem with the flue extraction fan. When this fault triggers, the boiler first runs the fan at full speed for up to 20 minutes in an attempt to clear the issue; if the problem persists, the boiler locks out and displays code 612 permanently. The fault belongs to the 600–699 ventilation error family and means the boiler cannot confirm the fan is spinning at the correct speed — it may be running too slowly, not at all, or the PCB may not be receiving a reliable speed-feedback signal. Because the extraction fan is critical for safely venting combustion gases out of the property, the boiler shuts down as a precaution. This is a safety lockout that should never be overridden or bypassed.

Causes, fixes & costs for Chaffoteaux 612 → · All Chaffoteaux codes

Frequently asked questions

Is the 612 fault code the same on every boiler?

Broadly, yes — on Ariston, ATAG and Chaffoteaux the 612 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 612 fault myself?

Not usually. On every brand listed, 612 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 612 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.