Hi, to anyone who can help me, please:-)?

I have a Baxi Bahama 100 combi boiler, to get a hot water, I need to wait long time for the hot water to comes on then it only give me hot water for a 10 - 15 Minutes then turn to cold again, have to wait another 10 or so minutes then the hot water comes on again and the cycle repeat is self.
by the way water is constantly running.

Any ideas, is my boiler on its last leg?