6P1 Boiler Fault Code: What It Means on Every Brand

The 6P1 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 6P1 means	Severity	DIY?
AAriston	The 6P1 fault code on Ariston boilers signals that the air pressure switch (also called the differential pressure switch or monostat) failed to close its contacts when the boiler attempted… Full guide →	Lockout — engineer likely	No
CChaffoteaux	The 6P1 fault code indicates that the boiler's control board has detected a delay or failure in the combustion air pressure switch (also called the combustion products pressure relay). Full guide →	Lockout — engineer likely	No

6P1 brand by brand

Ariston 6P1

The 6P1 fault code on Ariston boilers signals that the air pressure switch (also called the differential pressure switch or monostat) failed to close its contacts when the boiler attempted to start. In practice, this means the boiler's control board could not confirm that the fan was generating adequate airflow to safely extract flue gases, so the appliance locked out as a precaution. A closely related code, 6P2, carries the same underlying fault but triggers during normal operation rather than at start-up — both codes point to the same components and are diagnosed and repaired in the same way.

Causes, fixes & costs for Ariston 6P1 → · All Ariston codes

Chaffoteaux 6P1

The 6P1 fault code indicates that the boiler's control board has detected a delay or failure in the combustion air pressure switch (also called the combustion products pressure relay). In plain terms, the boiler cannot confirm that the fan is generating sufficient airflow and flue draught to remove exhaust gases safely before ignition begins. As a protective measure, the boiler locks out rather than attempt to fire. Some sources also describe 6P1 as a combustion parameter fault, meaning the boiler's electronics have detected that the burner's combustion settings are outside safe limits — either way, the root cause nearly always involves the fan, flue path, or the pressure switch circuit itself.

Causes, fixes & costs for Chaffoteaux 6P1 → · All Chaffoteaux codes

Frequently asked questions

Is the 6P1 fault code the same on every boiler?

Broadly, yes — on Ariston and Chaffoteaux the 6P1 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 6P1 fault myself?

Not usually. On every brand listed, 6P1 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 6P1 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.