Ariston boiler error 501

Error 501 indicates a flame issue. Be sure the gas valve is open. If it is, check the ionization electrode. If it is soaked, dry it using a dryer. Make sure that the distance between the electrode and the burner is at least 8 mm (±1 mm) and bend it if necessary. Also, be sure that there is a good connection between the electrode and the main control board.