Ariston Clas One error 501: no flame detected

What Does Error 501 Mean?

On the documented Ariston Clas One family, error 501 is a non-volatile lockout because flame was not detected. The boiler does not restart automatically and the user manual permits reset-button attempts, capped at five within 15 minutes. A returning 501 requires authorised technical service, not continued resetting. Applies to: Clas One and Clas System One condensing gas boilers This definition applies to Clas One and Clas System One user literature linked by Ariston. Nimbus heat pumps, Nuos water heaters, other One-series generations, and regional gas configurations need their own manual. Owner-safe checks: Photograph 501 and the model, check whether other gas appliances operate, and observe sounds only from outside the sealed case. Qualified technician: Gas supply pressure, valve, ignition, burner, flame signal, electrode, grounding, flue, condensate, control, and sealed-case work require authorised qualified service.