No green burner indicator on ?

Hello, I have a Worcester Greenstar Ri. Last few days have had the heating off and only hot water on. Last night turned heating on via timer contreol and after 10 mins or so noticed that heating didn't come on. I checked timer - all ok, then checked boiler. It was warm to the touch - but cooling. The green (pilot?) indicator was off but blue light was on. I reset with thermo switch then turned on max. Boiler green light came on... bolier began to fire up but then 10-15 seconds later the green light went out, the boiler shut down and the blue indicator inthe middle started flashing....any ideas?