Biasi M90E 32s cuts out after about 15-25 minutes?

My biasi m90e 32s cuts out after about 15-25 minutes, niether hot water or heating work. There is good pressure (1bar when off 1.5 on) and the fan continues to work for a further 5-10 minutes then the boiler ignites again, sometimes. The problem seems to be getting worse as the hot water temperature is now fluctuating. the boiler is only 14 months old and replaced one that was 20 years old and gave very few problems although admitedly wasnt the most efficient.