The boiler doesn't want to start up?

Hello, we have the worcester- bosch 24i- junior boiler. There is a pressure of 1 bar, the boiler is filled with water as normal. It has been used as normal, but suddenly the hot water stopped running and the red light started to flash very fast. We think there is not gas coming into it, but the gas pipe is on. Please would you advice us what to do. Thank you very much, regards Zofie