1P4 Boiler Fault Code: What It Means on Every Brand

The 1P4 fault code appears on 3 brands — Ariston, ATAG and Chaffoteaux — and it does not mean the same thing on each. The same two or three characters can signal a pressure problem on one boiler and an ignition fault on another, so identify your brand first and use the table below to jump to the right page.

Up to: Lockout — engineer likely 3 brands use this code Meaning differs by brand

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 1P4 means	Severity	DIY?
AAriston	The 1P4 code on an Ariston boiler is an early-warning alert rather than a hard lockout. Full guide →	Engineer may be needed	Some checks
AATAG	The 1P4 fault code on an Atag boiler (also displayed as F1P4 or fault code 108) indicates that the system water pressure has dropped below 0.8 bar — the minimum threshold the boiler needs… Full guide →	Lockout — engineer likely	Some checks
CChaffoteaux	The 1P4 fault code (also shown as F1P4 or sometimes referenced as fault 108 on certain Chaffoteaux models) indicates that the water pressure in the primary heating circuit has fallen below… Full guide →	Engineer may be needed	Some checks

1P4 brand by brand

Ariston 1P4

The 1P4 code on an Ariston boiler is an early-warning alert rather than a hard lockout. It signals that the boiler has detected either a drop in system water pressure below its alarm threshold (linked internally to parameter 241 and sometimes displayed alongside Error 108) or insufficient circulation around the heating circuit. Think of it as your boiler raising its hand before the situation worsens into a full lockout fault — codes 1P1 through 1P4 represent escalating stages of the same circulation or pressure problem, with 1P4 being the most serious warning stage before a true lockout is triggered. The boiler will usually continue to operate in a degraded state, but left unaddressed the underlying issue will almost certainly cause a full shutdown.

Causes, fixes & costs for Ariston 1P4 → · All Ariston codes

ATAG 1P4

The 1P4 fault code on an Atag boiler (also displayed as F1P4 or fault code 108) indicates that the system water pressure has dropped below 0.8 bar — the minimum threshold the boiler needs to operate safely. When your central heating system loses pressure, the boiler locks out as a protective measure rather than run dry. In most cases this is a straightforward fix: the system simply needs topping up via the filling loop to bring pressure back into the correct cold-fill range of 1.0–1.1 bar. Once the system heats up, it is normal for pressure to climb to around 1.8–2.4 bar — this is just water expanding with heat. However, if pressure drops repeatedly, an underlying fault such as a water leak, a weeping pressure relief valve, or a faulty pressure sensor is likely and will need professional attention.

Causes, fixes & costs for ATAG 1P4 → · All ATAG codes

Chaffoteaux 1P4

The 1P4 fault code (also shown as F1P4 or sometimes referenced as fault 108 on certain Chaffoteaux models) indicates that the water pressure in the primary heating circuit has fallen below the minimum threshold the boiler needs to operate safely. When pressure drops to this level, the boiler will stop firing and display 1P4 to protect itself and the system from damage. In many cases this is a straightforward fix — repressurising via the filling loop — but if the fault keeps returning, something else is causing the pressure to escape and a Gas Safe engineer will need to investigate.

Causes, fixes & costs for Chaffoteaux 1P4 → · All Chaffoteaux codes

Frequently asked questions

Is the 1P4 fault code the same on every boiler?

No. 1P4 means different things on different brands — see the table above. Always identify your boiler's brand (it is printed on the front casing) before acting on any advice about the code.

Can I fix a 1P4 fault myself?

On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. Where the code is a simple pressure or reset condition, that may be all it needs. Never open the boiler casing yourself.

Who should I call about a 1P4 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.