my gas fired central heating ?

check that the valve on the outlet side is open/partially It should be partly closed to restrict flow and balance the flow to the other radiators.
close down two radiators and see if the flow increased to the remaining radiator. If you are getting water when bleeding then the radiator is full-- you may have to balance the flow by using the lock shield restrictor on the return side of the rad.--failing that if they are old they could have corrosion inside.

tom
January 2010