I have an ideal isar HE30 condenser boiler no heating?

for the past few days when i put the heating on the display on my boiler has a C where the status is and the burner light flashes continuously, I have no heating but do have hot water, I have tried pressing the reset button which seemed to work as the boiler started firing up but then went straight back to the flashing light and no heating, any ideas what i can do? thanks