I have a biasi boiler every thing seems to work but when running the hot water or heating it seems to switch off then back on 4-5 seconds later is this usual,or is there a problem
are you saying that this problem occurs with both the hot water and heating?
if it was just the hot water or just the heating i would have plumped for a dodgy thermister, possibly diverter valve or pump.
if its happening on both then it could be the air pressure switch, the circuit board, overheat stat or a flue problem or pump