Open vented systems
For sealed systems, seek the services of a professional heating engineer
The connection between the valves and the radiator is of the compression type. It is, however, possible that with age the fitting may be a little worn. In this case you can render it watertight using one of the following methods.
Preparing the connections
Wrap a short length of PTFE tape around the thread in a clockwise direction before assembly. Or -
Smear a little jointing compound around the thread before assembly.
Both of these will take up any small gaps in the threaded section helping to seal the connection.
Lift the radiator up onto its brackets.
Manoeuvre the valve assembly at both ends so that they sit squarely onto the radiator connections.
Hand tighten the nut onto each valve, taking care not to cross thread them.
Tightening the valves
Holding the valve assembly with a pipe wrench so that it cannot be pulled off the pipe, use a second wrench to do up the connecting nut. This should be just tight enough to render the connection watertight. Excessive tightening may damage the fitting. Remember, you can tighten a joint if it leaks, but if it has been overtightened, you will need to dismantle it and start again.
Filling the radiator
Having tightened both connections, open the bleed valve at the top of the radiator.
Now open only the flow valve at the bottom of the radiator. This will be the valve used for turning the radiator on and off. This will allow the water to flow in, and air to be pushed out at the top.
When the water starts to splutter from the bleed valve, close it.
Now open the return valve at the bottom of the radiator by the same number of turns used to close it originally allowing water to circulate through the system once more whilst maintaining the origanal balance of flow.
Having left the return valve closed until the radiator is full, you will have prevented air from being pushed round into the rest of the system.
Check both connections for leaks before allowing the heating to be turned on again.