Why does my Biasi combi boiler central heating pump run constantly?

I am not sure if this is normal or not, but mr combi boiler's pump runs constantly when on. It turns on and off during the times programmed but I wondered weather it was supposed to pump the water around ther circuit even when the burner isn't on as the water is at the correct temperature and doesn't need heating so the burner goes off. Anyone help would be much appreciated.

Regards