You may have some air in the system and it is not actually moving the water. An air lock can cause this. First thing I'd try is to bleed it to see if there is any trapped air. I don't know the specifics of this boiler installation, but many call for a primary/secondary loop. How is yours installed? When the call for heat occurs, are the circulator(s) actually coming on? Do you have an air extraction device? Is it gunked up and no longer functioning? If you have zone valves, are the valves actually opening? Many of those have a manual override, you could try manually opening the one that is calling for heat. How many zones do you have? How about an indirect WH? If you have one, is that warming up properly, or does it fail when that zone calls for heat as well?