Worcester green star Ri blue light flashing?

Hi, had someone look when the boiler would not come on at all, they said main Pcb and transformer. I have replaced these and now the blue light comes on fan starts and sounds like it ignites, runs for about 1 to 2 mins then stops with the blue light flashing about 2 seconds on and 2 seconds off, I move dial to reset which it does then all the same things again. Pump sounds like it's running and pipe from it after resetting a few times is not anywhere near as cold as the others. Any advice on what the blue light is telling me? Please help!