Like taps, radiators can develop leaks. Fortunately, these are usually really easy to fix. If you are not sure how to fix a leaking radiator valve, watch this video tutorial to learn how.
Before you start - get a spanner, some paper tissue, and some PTFE tape.
Water leaking from a radiator valve might be seeping from around the valve spindle. However, when the water runs round and drips from the valve's cap-nut, it's the nut that often appears to be the source of the leak. Dry the valve then hold a fresh piece of paper tissue against the various bits to work out exactly where the moisture is coming from.
To stop a leak from a radiator-valve spindle, tighten the gland nut with a spanner. If the leak persists, undo the nut and wind a few turns of PTFE tape down into the spindle.
If the cap-nut is leaking, tighten it gently with a spanner. In most cases this will stop the leak. However, if the leak persists, you will need to replace the valve.