My boiler won't work properly?

I have a Worcester Greenstar CDI combi boiler which is around 5 years old. This week it has started playing up. it keeps going off and won't fire back up, display has EA on it. Our usual fix in the cold weather was to pour a kettle of hot water on the outlet pipe outside, however this did not work this time, i found a post on a website that suggested removing the white flexi pipe from the underside of the boiler to drain it. I did this and got approx 2 pints of water out of it, reset the boiler and it worked fine. but, it goes off again every half an hour or so and i have to repeat the draining process. can anyone help me?