1P3 Boiler Fault Code: What It Means on Every Brand

The 1P3 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 1P3 means	Severity	DIY?
AAriston	The 1P3 code on an Ariston boiler is an early-warning indicator that water is not circulating properly around the central heating system. Full guide →	Engineer may be needed	No
AATAG	The ATAG 1P3 fault code indicates a repeated 'Flow Check Failed' condition. Full guide →	Lockout — engineer likely	Some checks
CChaffoteaux	The 1P3 code appears on Chaffoteaux boilers when the boiler detects a circulation problem in the primary heating circuit. Full guide →	Engineer may be needed	Some checks

1P3 brand by brand

Ariston 1P3

The 1P3 code on an Ariston boiler is an early-warning indicator that water is not circulating properly around the central heating system. Unlike a hard lockout code, the boiler may still be running when this appears, but it is alerting you to a circulation problem that needs attention before it escalates into a more serious fault. The 1P series codes (1P1, 1P2, and 1P3) all point to the same underlying issue — insufficient circulation — and apply across all Ariston boiler models. If left unaddressed, 1P3 typically progresses to a full lockout in the 103–107 fault code range, at which point the boiler will shut down completely. Acting on 1P3 early can save you from a cold home and a more expensive repair.

Causes, fixes & costs for Ariston 1P3 → · All Ariston codes

ATAG 1P3

The ATAG 1P3 fault code indicates a repeated 'Flow Check Failed' condition. Specifically, it is triggered when the boiler detects three occurrences of a 1P1-type flow error within a 15-minute window. A 1P1 event occurs when the boiler's supply (flow) temperature rises by between 7°C and 15°C in a single second — a spike that points to water circulation dropping sharply through the heat exchanger. When this pattern repeats three times in quick succession, the boiler escalates to 1P3 and locks out to protect itself from overheating. In plain terms: water is not moving through the boiler quickly enough, so heat is building up dangerously fast. The 1P3 code is part of the broader '1P' fault family on ATAG i Series (2nd and 3rd generation) boilers, which includes 1P1 (single flow check event), 1P2, 1P4, and 1P9. If you are seeing 1P1 or 1P2 on your display instead, the underlying cause and the diagnostic approach are broadly the same as described here.

Causes, fixes & costs for ATAG 1P3 → · All ATAG codes

Chaffoteaux 1P3

The 1P3 code appears on Chaffoteaux boilers when the boiler detects a circulation problem in the primary heating circuit. The trigger condition is that the return water temperature (Trit) has climbed to more than 10°C above the flow temperature (Tman), which tells the boiler that hot water is not moving freely around the circuit as it should. The '1' prefix in all Chaffoteaux 1Px codes identifies the primary heating circuit as the affected zone. Codes 1P1, 1P2, and 1P3 all belong to the same fault family — insufficient primary circuit circulation — with 1P3 representing the third stage of escalation within that group. Unlike a hard lockout, 1P3 is a warning-level notification, meaning the boiler may continue to attempt operation rather than shutting down entirely. A related hard-fault code, 103, covers the same underlying circulation failure but will stop the boiler completely.

Causes, fixes & costs for Chaffoteaux 1P3 → · All Chaffoteaux codes

Frequently asked questions

Is the 1P3 fault code the same on every boiler?

No. 1P3 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 1P3 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 1P3 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.