5P4 Boiler Fault Code: What It Means on Every Brand

The 5P4 fault code appears on 2 boiler brands — Ariston and Chaffoteaux — and on all of them it points to the same kind of problem. The details still differ by brand (thresholds, sub-codes, reset procedure), so use the table below to jump to the page for your boiler.

Lockout — engineer likely 2 brands use this code

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 5P4 means	Severity	DIY?
AAriston	The 5P4 code appears when your Ariston boiler has attempted to ignite or hold a flame three times within a single working cycle and failed every time. Full guide →	Lockout — engineer likely	No
CChaffoteaux	The 5P4 code appears on Chaffoteaux boilers after four consecutive failed attempts to ignite the burner. Full guide →	Lockout — engineer likely	No

5P4 brand by brand

Ariston 5P4

The 5P4 code appears when your Ariston boiler has attempted to ignite or hold a flame three times within a single working cycle and failed every time. After that third failure the boiler locks itself out and will not restart automatically. It sits at the end of a family of escalating codes — 5P1 (one failed attempt), 5P2 (two failed attempts), and 5P3 (flame cut-off) — with 5P4 representing the point at which the boiler gives up and shuts down for safety. Until the underlying cause is resolved and the boiler is reset, it will remain locked out.

Causes, fixes & costs for Ariston 5P4 → · All Ariston codes

Chaffoteaux 5P4

The 5P4 code appears on Chaffoteaux boilers after four consecutive failed attempts to ignite the burner. Chaffoteaux boilers run through a structured ignition-attempt sequence — 5P1 through 5P6 — where each code represents one more failed try. If the boiler lights on the second attempt, it stops at 5P2 and carries on normally; if it keeps failing, the code steps up through 5P3 and then 5P4. By this stage the boiler has given up and locked out, meaning it will not restart by itself and needs a manual reset. Note that the digit '5' on the display closely resembles the letter 'S', so many users read this code as 'SP4' rather than '5P4' — both refer to the same fault. Because this is a non-volatile lockout, power cycling alone will not clear it; you must press the reset button on the front panel.

Causes, fixes & costs for Chaffoteaux 5P4 → · All Chaffoteaux codes

Frequently asked questions

Is the 5P4 fault code the same on every boiler?

Broadly, yes — on Ariston and Chaffoteaux the 5P4 code points to the same class of fault, and the recommended response is similar. Model-specific details such as sub-codes and reset procedures still vary, so follow the page for your own brand.

Can I fix a 5P4 fault myself?

Not usually. On every brand listed, 5P4 points to a fault that needs a suitably registered engineer to diagnose and repair. A single reset to rule out a transient glitch is reasonable; repeated resets are not.

Who should I call about a 5P4 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.