The 1P2 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.
The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.
| Brand | What 1P2 means | Severity | DIY? |
|---|---|---|---|
A Ariston | The 1P2 code appears on Ariston boilers when the boiler's internal sensors detect that water is not moving around the heating system as freely as it should be. Full guide → | Engineer may be needed | No |
A ATAG | The 1P2 code is a safety lockout triggered when the boiler detects that the temperature difference between its flow (T1) and return (T2) pipework has exceeded 55°C. Full guide → | Lockout — engineer likely | Some checks |
C Chaffoteaux | The 1P2 code on a Chaffoteaux boiler indicates that the boiler has detected inadequate water circulation through its heating body. Full guide → | Lockout — engineer likely | Some checks |
The 1P2 code appears on Ariston boilers when the boiler's internal sensors detect that water is not moving around the heating system as freely as it should be. Unlike a hard lockout code, 1P2 is an early warning — the boiler is flagging a circulation problem before it escalates into a more serious fault (such as codes 103–107). In plain terms, water flow through your system is restricted or sluggish, and the boiler wants you to investigate before things get worse.
The 1P2 code is a safety lockout triggered when the boiler detects that the temperature difference between its flow (T1) and return (T2) pipework has exceeded 55°C. This abnormally large differential tells the boiler that water is barely circulating through the heat exchanger, putting it at serious risk of overheating. ATAG groups three related flow-check codes together in the i Series: 1P1 fires when the flow temperature jumps by 7–15°C in a single second; 1P2 escalates when the flow-to-return differential breaches that 55°C threshold; and 1P3 triggers when three 1P1 events occur within a 15-minute window. If your display shows 1P2, the boiler has already moved beyond the first-level warning and shut itself down to avoid heat exchanger damage.
The 1P2 code on a Chaffoteaux boiler indicates that the boiler has detected inadequate water circulation through its heating body. In plain terms, the boiler is not seeing enough flow to operate safely, and has locked out to protect itself from overheating. This fault sits within the '1xx' family of errors on Chaffoteaux Expert Control models — a group that covers pressure and flow-related problems including overheat conditions, pressure sensor faults, and various flow-check failures. The 1P2 code specifically points to a circulation failure, which can stem from low system pressure, a faulty pump, blockages in the system, or a sensor problem. The boiler will not fire until the underlying cause is resolved.
Causes, fixes & costs for Chaffoteaux 1P2 → · All Chaffoteaux codes
No. 1P2 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.
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.
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.
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