Boiler Ferroli Modena 102 problems with condensation?

I've been having a lot of problems with my boiler recently. It seems to fire up but actually doesn't no warning lights or anything. I have had a repairman out three times:

- first time replaced the venturi and worked fine

- second time he emptied water that had collected from the flue and suggested the flue wasn't angled correctly

- third time had a guy out to measure the downfall of the flue and it is correct, and the guy just blew in a tube to get the boiler to work again

Well it's now broken down for a 4th time and I would really appreciate some help as to what it might be. The apartment is brand new, 5 months old and the first problem occurred after 4 months, then it has broken down ever since. Thanks