For sealed systems, seek the services of a professional heating engineer
Joints in pipework
Soldered joints which have sprung a leak will need to be replaced. Drain the system and replace the joint by following the section on soldered joints.
Compression joint leaks can sometimes be cured by a slight tightening of the nut.
Remember to hold the other nut with a spanner or wrench to prevent pulling the joint from the pipe.
Tighten the leaking side a small amount and no more than a quarter turn. More than this and you’ll damage the joint. If this is not successful, you’ll need to drain down the system and refit the joint. Refer to compression fittings in the plumbing section.
Radiators can develop pinholes. This is caused by corrosion due to sludge or excessive air getting into the system. The air actually promotes corrosion. The only satisfactory cure is to remove the radiator and fit a new one. Be sure however to flush the system through and identify whether air is getting into the system.
Failure to resolve the cause may mean you’ll get very used to replacing radiators!
If the valve leaks where it connects to the pipework, you will need to repair the joint. The system will need to be drained down and the joint redone. This is a compression type joint and relies upon a metal collar known as an olive to make the seal when the nut is tightened. For details on how to make this type of connection see compression fittings in the plumbing section.
If the leak is the other side of the valve where it goes off to the radiator, you can turn off both valves and drain just the radiator in question. Whilst you won’t need to remove the radiator, you’ll find details on emptying it in the removing a radiator section. Undo the connection, and wind a length of PTFE tape around the joint before reassembling and you’ll find that this will help to seal the thread and stop any leaks. Open the air vent and then open just the flow valve. Allow the radiator to fill and close the air bleed valve when water begins to come out. Now open the return valve.
Follow the same procedure above to empty the radiator. Disconnect the radiator from the valve first, then use a large Allen key inserted in the end to undo the radiator connector. Then clean the thread and wrap a length of PTFE tape around it. Refit the connector to the radiator doing it up with the Allen key, and reconnect the valve.
Air bleed valve
Partially drain the radiator so that the water level inside is at least below the level of the air bleed valve. Using an Allen key inserted into the valve, you can undo and remove it. Clean the thread and wrap a little PTFE tape around it before reinserting and tightening it back up. Refill the radiator.
The gland nut at the base of the spindle of a valve sometimes works loose.
Holding the valve assembly with a pipe wrench to prevent it being pulled from the pipework, use a spanner to tighten the nut a little. If this doesn’t do the trick, it indicates that the gland packing has become worn. Turn off both valves and undo the gland nut. Using a length of special gland packing, wind a few turns around the base of the spindle and pack it in tightly using a small screwdriver. Replace and retighten the gland nut. Open one valve at a time and check again for leaks.