what wrong with combi boiler?

I have breath all cenral heating in my house so heating can be flow fully inside the rediator, after that the boiler pressure went very low (0), i managed to bring pressure to normal(1 bar), now there is no hot water, but i can hear boiler turning on when the hot water open/ central heating turn on, i can't figure it out what wrong even i can hear bailer flame. could you please advice me.
thank you (combi boiler Worcester 28i)