how can i fix my central heating?

We have recently switched on our central heating for the winter with little success. Initially, when the boiler is switched on it ignites and seems to be fine for a few minutes. It then trips off. With a hissing and slight banging noise. I tried to bleed the radiators and an awful lot of air came out. The downstairs radiators are now full of water. However, the upstairs ones ceases expressing air and no water emerged. Simply nothing. Each time i try to put the heating on it trips off again and the upstairs radiators, when bled, hiss again for a few seconds then silence. I have checked the pump and it is spinning. Also when the electric is heating the tank the system works fine for hot water.