The 1P1 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 1P1 means | Severity | DIY? |
|---|---|---|---|
A Ariston | The 1P1 code is Ariston's early-warning signal that water isn't flowing through the heating system as well as it should be. Full guide → | Engineer may be needed | Some checks |
A ATAG | The 1P1 fault code appears on Atag i Series boilers when the control system detects that the flow water temperature is climbing too rapidly — typically a rise of between 7°C and 15°C… Full guide → | Engineer may be needed | No |
C Chaffoteaux | The 1P1 code on Chaffoteaux boilers signals an anomaly in the central heating circuit, most commonly linked to insufficient water pressure or a flow-check failure. Full guide → | Lockout — engineer likely | Some checks |
The 1P1 code is Ariston's early-warning signal that water isn't flowing through the heating system as well as it should be. Unlike a hard lockout, the boiler is still attempting to run but has detected circulation levels below what it expects. Think of it as the system raising a hand before the problem gets serious — related codes 1P2, 1P3, and 1P4 represent progressively worse stages of the same underlying issue. Catching and addressing 1P1 early can prevent a full boiler lockout.
The 1P1 fault code appears on Atag i Series boilers when the control system detects that the flow water temperature is climbing too rapidly — typically a rise of between 7°C and 15°C within a single second. This strongly suggests that water is not circulating quickly enough through the heat exchanger, causing the small volume of water present to overheat almost instantly. Atag labels this internally as a 'flow check failed' condition. If the same event happens three times within a 15-minute window, the boiler will escalate to a full lockout rather than attempting another restart, so it is important to identify and resolve the underlying cause promptly rather than repeatedly resetting.
The 1P1 code on Chaffoteaux boilers signals an anomaly in the central heating circuit, most commonly linked to insufficient water pressure or a flow-check failure. It is worth noting that Chaffoteaux displays can sometimes be misread — the code may also appear as 103 or 104 on certain models (flow check failed), while related codes include 102 (pressure sensor error) and 108 (filling needed). All of these point broadly to the same heating-circuit pressure fault family. Chaffoteaux is part of the Ariston Thermo Group, so the underlying logic is shared across several models. When the boiler detects that pressure in the heating circuit has dropped below the safe operating threshold — or that the pressure switch is not communicating with the control board — it locks out and displays 1P1 to prevent damage.
Causes, fixes & costs for Chaffoteaux 1P1 → · All Chaffoteaux codes
No. 1P1 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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