domestic hot water works but the heating shuts down?

.hello i have a halstead ace boiler, the hot water works fine but the heating shuts down after a few mins....there is then a green flashing light,on the heating...the pump turns freely when i unscrew the screw at the front, i've tried tapping the pump with a hammer to free any silt....is there a separate fuse for the pump??...i've just bought the house & its been empty for about a year....any ideas??