How to stop it flashing L 3 Logic Combi 24 Boiler?

Hello All....Help Please.
My Logic Combi 24 Boiler is flashing L 3. The manual Fault Codes Reads: No Water Flow. How on earth can I safely remedy this? It's just over a year old and it packed up after 2 months....had nothing but trouble with it. Any help in Simple Terms non technie would be great!

With Thanks