hot water going cold

[mdbuild]

i,ve got a problem with the hot water ,when hot water is running either in shower or sink it will remain hot for a period of time e,g 1-2 minutes then the pilot on the boiler will turn out then reignite this happens during the use of the hot water,central heating is working fine,its a combi boiler the make is ferroli modena 102 approx 4yrs old,
any ideas many thanks

 

[petit_pablo]

Without being able to check flow rates and temps id say that the heat isnt being transfered very well causing the boiler to go cycle on and off.