fuses blown on ariston type c combi boiler?

Ariston Microgenus HE 24 Combi-boiler. The boiler is about 2 years old and it has started blowing fuses. All was well until last week when I looked at it the power light was off. I checked out the system and found the two 2 amp fuses on the PCB blown. The fused spur was still ok. I have since replaced the fuses and the boiler fires up for a while and then there is a flash as the fuses blow again. I replaced the fuses again and the same happend, I then installed delay fuses and the boiler worked fine for a week until this morning. I have istalled another set of delay action fuses it seems to be working ok but why did it blow?

nash
January 2012