A 01 - means ignition failure, as the boiler was sparking/trying to light, the first thing to check is the gas supply, then see if there's power to the gas valve.
What does A 79 mean ??? read the manufacturers instructions.
I was going to google it - but I shouldn't have to. You need to give as much info as possible - plus Ariston's are crap, not many people have them, so no-one knows the fault codes :-) - but I would have checked the gas valve before buying a new PCB.
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