5P3 Boiler Fault Code: What It Means on Every Brand

The 5P3 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 5P3 means	Severity	DIY?
AAriston	The 5P3 fault code on Ariston boilers indicates that the burner flame went out while the boiler was already running — as opposed to a failure to ignite in the first place. Full guide →	Lockout — engineer likely	No
CChaffoteaux	The 5P3 fault code on a Chaffoteaux boiler indicates that the flame was detected as having gone out unexpectedly while the boiler was mid-cycle — the burner lit and ran normally, but the… Full guide →	Lockout — engineer likely	No

5P3 brand by brand

Ariston 5P3

The 5P3 fault code on Ariston boilers indicates that the burner flame went out while the boiler was already running — as opposed to a failure to ignite in the first place. The boiler managed to light successfully, but something caused the flame to extinguish mid-operation, triggering a safety lockout. This code sits within the 5P1–5P3 family of flame-related faults on Ariston appliances: 5P1 typically relates to a failure to ignite on first attempt, 5P2 to repeated ignition failure, and 5P3 specifically to flame loss once the burner is already alight. The control board monitors the flame signal continuously via an ionisation probe; if that signal drops away unexpectedly, the board locks the boiler out and displays 5P3.

Causes, fixes & costs for Ariston 5P3 → · All Ariston codes

Chaffoteaux 5P3

The 5P3 fault code on a Chaffoteaux boiler indicates that the flame was detected as having gone out unexpectedly while the boiler was mid-cycle — the burner lit and ran normally, but the flame then cut out before the heating or hot water cycle was complete. As a safety measure, the boiler shuts itself down entirely to prevent unburned gas from accumulating, which could otherwise cause a carbon monoxide or fire hazard. A note on the display: because the digit '5' on Chaffoteaux displays closely resembles the letter 'S', many users read this code as SP3 rather than 5P3 — both refer to the same fault. If 5P3 occurs repeatedly without being resolved, the boiler may escalate to fault code 504, which signals a burner ionisation anomaly after multiple successive 5P3 events. On Urbia and Pigma models, 5P3 can also appear as a general start-up or boot problem rather than a mid-cycle flame loss.

Causes, fixes & costs for Chaffoteaux 5P3 → · All Chaffoteaux codes

Frequently asked questions

Is the 5P3 fault code the same on every boiler?

Broadly, yes — on Ariston and Chaffoteaux the 5P3 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 5P3 fault myself?

Not usually. On every brand listed, 5P3 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 5P3 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.