Ariston Clas Fault Codes
The Ariston Clas — from the Clas HE era through today's Clas One — is the Italian brand's core UK combi and system range. Ariston reports faults as three-digit codes grouped by hundreds: 1xx for heating-circuit faults (101 overheat, 108 insufficient pressure), 3xx for electronics, 5xx for ignition and flame detection (501 no flame the classic), 6xx for air/flue, and 1P/5P-prefixed codes for pre-lockout anomalies the boiler flags before they harden into faults. That structure is genuinely useful once known: the first digit tells you the neighbourhood before you look anything up. The Clas One generation adds a clearer display and quieter running, but speaks the same code language. Each code below links to its full cause-and-fix page.
Where Clas fault codes appear
The Clas shows its three-digit code on the fascia display when a fault trips — the Clas One on a clearer segment display than the older HE. Codes prefixed 1P or 5P are anomaly warnings rather than hard lockouts; note them exactly as shown, prefix included.
Resetting a Ariston Clas
Press the reset button briefly; the boiler clears and retries. Code 108 wants the system topped up to 1–1.5 bar via the filling loop first. Ariston limits consecutive resets on flame faults by design — a 501 that returns after one reset is a diagnosis (gas supply, condensate, electrode…), not a button-pressing exercise.
Common Clas problems
Clas owners chiefly meet 108 (pressure — top-up territory), 501 (no flame, with the winter condensate freeze and gas-supply checks first), 101 overheats where circulation is compromised, and 5P1/5P2 ignition anomalies foreshadowing a proper 501. Sludge management and an annual service keep the 1xx codes rare; electrodes and gas-valve wear account for most 5xx visits.
Most common Clas fault codes
- 501 Fault code 501 on an Ariston boiler means the boiler attempted to light the burner but… Read more →
- 108 Fault code 108 on an Ariston boiler indicates that the water pressure inside the central… Read more →
- 101 Fault code 101 on an Ariston boiler indicates that the central heating circuit has… Read more →
- 104 Ariston fault code 104 is a safety lockout triggered when the boiler detects that water… Read more →
- 5P1 The 5P1 code appears on Ariston boilers when the burner fails to ignite on the first… Read more →
- 307 Fault code 307 on an Ariston boiler signals an internal fault with the electronic control… Read more →