Find the exact wet point before touching the valve
Radiator valves can leak from several places that are only a few centimetres apart. Water around the spindle under the valve cap suggests a packing or gland issue. Moisture at the compression nut on the pipe side points towards that joint. A leak where the valve screws into the radiator can involve the threaded tail connection. Dry the area and wrap separate pieces of tissue around each point. The first one to become wet is a much better guide than the puddle on the floor.
Thermostatic valves have extra moving parts
A thermostatic radiator valve, often called a TRV, has a removable head and a valve body beneath it. Water does not normally pass through the plastic control head itself, so wetness there has usually travelled up from the spindle area. A stuck pin can stop the radiator heating, but that is a different fault from a water leak. Avoid unscrewing large nuts on a live heating system simply to investigate; opening the wrong connection can release far more water than the original seepage.
Small leaks can mark floors quickly
Heating water often contains inhibitor and can leave dark or rusty stains on carpet, timber and decoration. A slow drip may only appear while the system is hot because expansion changes the joint slightly. Check the valve both when the heating is cold and after the radiator has warmed. If the leak is above a finished floor, protect the area while waiting for repair. A valve that is badly corroded or has already been tightened several times is more likely to need replacement than another small adjustment.
System pressure matters on sealed heating systems
If the heating system has a pressure gauge, a leaking valve can contribute to a gradual pressure drop. Repeatedly topping up the boiler without addressing the leak introduces fresh oxygenated water and does not solve the cause. A very small seep may not change the gauge noticeably, but a persistent leak should still be repaired. If pressure is falling quickly or water is escaping continuously, switch the heating off and seek help rather than trying to compensate by adding more water.
What a plumber may repair
A minor spindle leak can sometimes be cured by servicing the gland, while a leaking compression joint may be remade if the pipe and fitting are sound. Corroded, damaged or troublesome valves are often better replaced. Replacing a valve may require draining part or all of the heating circuit unless freezing or other suitable methods are used. After the work, the system may need repressurising, bleeding and checking for leaks as it warms. The price therefore depends on more than the cost of the valve itself.
Information that helps with a quote
Say whether the valve is thermostatic or a simple manual type and which side of the radiator is leaking. Mention whether the system loses pressure and whether the leak changes when the heating is on. A close photograph of the valve and a wider shot showing the radiator are useful. If the pipe comes through a solid floor or is difficult to access, include that detail. Ask whether the quotation includes draining, refilling and any inhibitor that may be needed after the repair.
Protect the floor while you arrange the repair
A folded towel may catch a few drops, but heating water can stain pale carpet and timber, so use a waterproof tray or suitable protection if the valve is still seeping. Do not wrap the whole valve so tightly that you can no longer see whether the leak is worsening. If boiler pressure is falling, note the gauge reading when the system is cold and avoid constant topping-up just to keep it running. When the plumber has repaired the valve, ask for the joint to be checked again after the radiator warms because heat can reveal a connection that looked dry when cold. If a new valve has been fitted, make sure the radiator heats properly and that the system pressure has been returned to its normal range.
This page is general guidance about leaking radiator valve; the cause in an individual home still needs to be established from the actual installation.