I have a heatline viso 24 combi condensing boiler which i have recently installed about a month ago. I flushed the system when i installed the new boiler. Everything has been working fine until now. When i turn on hot water tap boiler fires ,runs until water gets quite hot then flame dies down and cuts out. boiler will refire after about 10 seconds which leaves me with cooler water when the boiler is not running. Any ideas? i have called heatlines technicial dept they say sounds like a blocked heat exchanger, but the water still flows really well. Could it be the water temp sensor in the boiler?