706 Boiler Fault Code: What It Means on Every Brand

The 706 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 706 means	Severity	DIY?
AAriston	Fault code 706 appears on Ariston E-Combi Evo, E-System Evo, Clas HE Evo Combi, and Clas HE Evo System boilers when the second heating zone has exceeded its safe temperature threshold. Full guide →	Lockout — engineer likely	Some checks
CChaffoteaux	On Chaffoteaux boilers, '706' is not a conventional three-digit numeric code. Full guide →	Lockout — engineer likely	No

706 brand by brand

Ariston 706

Fault code 706 appears on Ariston E-Combi Evo, E-System Evo, Clas HE Evo Combi, and Clas HE Evo System boilers when the second heating zone has exceeded its safe temperature threshold. The boiler performs a safety lockout to protect the system from heat damage and to prevent scalding. Until the underlying cause of the overheating is resolved, the boiler will not restart normally. Note: if you own an older Ariston model such as the Clas One, Clas Net One, E-Combi (non-Evo), or E-System (non-Evo), the equivalent fault is code 722, which indicates the same Zone 2 overheat condition on those platforms.

Causes, fixes & costs for Ariston 706 → · All Ariston codes

Chaffoteaux 706

On Chaffoteaux boilers, '706' is not a conventional three-digit numeric code. These boilers use a flashing LED binary system, and what homeowners read as '706' is almost always the LEDs labelled 70 and 80 flashing together (sometimes also described as the 40+60+80 combination). This pattern points to a breakdown in communication between the fan and the air pressure switch (APS). Either the fan is running but the APS is not confirming adequate airflow to the PCB, or the fan is off but the APS has failed to return to its resting (off) position. In both cases the PCB cannot verify that harmful combustion gases are being safely expelled through the flue, so as a precaution it locks out gas flow and shuts the boiler down. Until the PCB receives a clean signal from the APS confirming the fan is working correctly, the boiler will not fire.

Causes, fixes & costs for Chaffoteaux 706 → · All Chaffoteaux codes

Frequently asked questions

Is the 706 fault code the same on every boiler?

Broadly, yes — on Ariston and Chaffoteaux the 706 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 706 fault myself?

On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. The underlying repair usually needs a registered engineer. Never open the boiler casing yourself.

Who should I call about a 706 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.