Baxi Bahama 100 Cutting Out?

I have a Baxi Bahama 100 Combi Unit, and recently it has started cutting out on me. When running the hot water it will ignite for about 1 minute, just enought time for the water to get hot, then it will cut out and the water will run cold. If I then turn the tap off and back on again, it will reignite and run for a minute and cut out again. The same applies to running the central heating. Whilst this is going on there seems to be a slight rush of water somewhere inside the boiler, but whether this is related I dont know. Can anyone help, as the weathers starting to get cold!