5P1 Boiler Fault Code: What It Means on Every Brand

The 5P1 fault code appears on 2 brands — Ariston 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 2 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 5P1 means	Severity	DIY?
AAriston	The 5P1 code appears on Ariston boilers when the burner fails to ignite on the first attempt. Full guide →	Lockout — engineer likely	No
CChaffoteaux	The 5P1 code on a Chaffoteaux boiler is a notification indicating that the boiler has failed on its first ignition attempt. Full guide →	Engineer may be needed	Some checks

5P1 brand by brand

Ariston 5P1

The 5P1 code appears on Ariston boilers when the burner fails to ignite on the first attempt. Because Ariston's seven-segment display renders the digit '5' in a way that closely resembles an 'S', many homeowners read this as 'SP1' — they are the same fault. The boiler is telling you it tried to light the burner and couldn't. Ariston uses a progression of these codes: 5P1 for the first failed attempt, 5P2 for a second failed attempt, and 5P3 for a third consecutive failure, at which point the boiler locks out completely and requires a manual reset before it will try again. Older Ariston models may display SP1 or SP2 rather than the newer 5P1 notation, but the underlying fault is identical. This is an ignition lockout notification rather than a sign of catastrophic failure — in many cases the cause is straightforward — but repeated occurrences always warrant investigation by a Gas Safe registered engineer.

Causes, fixes & costs for Ariston 5P1 → · All Ariston codes

Chaffoteaux 5P1

The 5P1 code on a Chaffoteaux boiler is a notification indicating that the boiler has failed on its first ignition attempt. It is worth noting that many users misread this code as 'SP1' because the digit '5' on the boiler's display can look like the letter 'S' — but 5P1 is the correct reading. The code itself is not a hard lockout fault in isolation; rather, it flags the first of a sequence of failed start attempts. If the boiler fails to ignite three times in succession, it will lock out completely and will not restart automatically. Because 5P1 is a non-volatile notification, the boiler must be manually reset before it will try to fire again. The most common triggers are a gas supply interruption, a dirty or mispositioned ignition electrode, or a blocked burner, though a faulty gas valve or PCB can also be responsible in more serious cases.

Causes, fixes & costs for Chaffoteaux 5P1 → · All Chaffoteaux codes

Frequently asked questions

Is the 5P1 fault code the same on every boiler?

No. 5P1 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 5P1 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 5P1 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.