how can i fix my Worcester 24i combi boiler?

when I turn on the hot water tap my boiler ignites and heats the water like it should, but after about 5 mins the boiler cuts out and the water runs cold, it then fires up again but then stops it keeps doing this and there is a clicking noise that seems to stop the burner as soon as it ignites. i then turn the hot water tap off and wait a minute whilst the clicking stops and try again turning the tap on but again it fires up then stops lots of clicking no hot water. i can try again after 10 mins and get about 5 mins of hot water then nothing.