underside Radiator leak

[Ed1981]

I found I had a dripping radiator last night. Stemming from under the radiator i think its called a pinhole leak??
I have turned thermostat off and turned the valve on rad fully clockwise.
The boiler has no pressure, when i refilled the boiler other rads ok. However isolated rad seemed to then drip more and continues to drip.
Just needing the rad to stop dripping and know that if water is going to the other rads that the isolated one wont fill again and start leaking.
Any help greatly appreciated

 

[steadyon]

1 The radiator will have two valves, normally one at each end.
2. You need to turn both off. If you only turn 1 off, water will flow into the radiator from the other, and drip out of the pin hole.
3. One valve will be what is called a lock-shield valve. It is used when balancing the system, but should otherwise not be touched unless turning the radiator off completely.
4. The other valve will be either a thermostatic radiator valve (larger head normally with numbers on it) or a wheel-head valve, which is very similar to a lock-shield, but with a cap, normally white plastic, to turn it on and off.
5. Lock-shield valves normally require a key or a spanner / pliers to open and close them. They often have a plastic cap which either pulls off or is held on by a central screw.
6. To close the lock-shield, remove any cap, then close it by turning with spanner, clockwise as you look down on it. As you close it count the number of 1/8 turns and make a note of the number. When you have finished changing the radiator, open the lock-shield the same number of 1/8 turns to preserve the system's balance.