Potterton sumprima amber light?

I have a suprima. When I put heating on the boiler will show a solid amber coloured light and not fire up. When I put the hot water on the boiler fires up like normal and displays the green light. When I put both of them on the boiler fires up and works like normal and displays a flashing light from green to amber. Heating still does not work. Anyone have any idea what this might be?