Ariston [303] fault codewhat it means and how to fix it

Codes beginning with 3 are the internal electronics group, and 303 is a main PCB error. Ariston use several adjacent numbers for related problems — 301 for an EEPROM error, 305, 306 and 307 for other board faults, and 313 for a low voltage fault — so the exact number matters when an engineer orders parts. A board fault is genuinely a board fault more often than not, but it is worth knowing that unstable mains supply produces board errors that look identical. A property with a marginal supply, a shared meter arrangement, or a history of brownouts can throw these codes without anything being wrong with the board itself, which is why Ariston list a separate low voltage code. It is also worth checking whether the appliance has been reset more than five times in fifteen minutes, because that produces a 304 rather than a 303 and is not a fault at all. Replacing a control board is one of the more expensive repairs on a domestic boiler, so it is reasonable to expect an engineer to eliminate the supply first.