Do this first
- Get a container under it and a towel round the pipe. Heating water is dirty and it stains carpet and timber permanently within an hour.
- Close both valves on that radiator. Turn the thermostatic head down to its off position or fit the plastic decorator's cap, then take the cover off the lockshield at the other end and close it clockwise with a spanner or pliers, counting the turns as you go so it can be reset to the same balance afterwards.
- If it still weeps with both valves shut, the leak is between the valve and the pipe rather than inside the radiator, and the next isolation point is the heating circuit itself.
- Do not top the boiler up repeatedly to hold pressure while it drips. You are feeding the leak.
- Dry the area and put fresh kitchen roll under the joint. The paper shows you within the hour whether isolation has actually worked.
- Keep the valve head, the packing nut cover and any small parts. Matching an obsolete valve is easier with the old one in hand.
Which part is actually leaking
Four places leak on a radiator valve and they are told apart by exactly where the water appears, not by how much of it there is. Dry everything, then watch for the first bead.
| Where the water forms | What it is | What it needs |
|---|---|---|
| Around the spindle, under the plastic head, and it gets worse when you turn the valve | The gland packing has dried out | Tighten the gland nut a quarter turn, or repack it. Minutes. |
| At the union nut where the valve meets the radiator tail | The olive or the tail joint has relaxed | Nip it up, or drain down and remake the joint |
| At the compression nut where the valve meets the pipe from the floor | Olive, or pipe movement from the floor below | Remake the joint, sometimes with a new olive |
| Weeping from the body of the valve itself, or from a green or white crust on the casting | The valve body is corroded or cracked | Replacement. Tightening makes a cracked body worse. |
The distinction that matters most is the last one. A weeping spindle or nut takes minutes and no drain-down. A corroded body or a rotted pipe tail is a replacement, and someone who tries to tighten their way out of it can crack a brittle casting and turn a drip into an open pipe in a room with a carpet. If the water is coming from the panel rather than either valve, that is a different fault: see a leaking radiator.
One more check worth doing while you are down there. If the pressure gauge on the boiler has been falling as well, this valve may not be your only leak. A boiler that keeps losing pressure is often losing it in two places at once.
Fixing a weeping spindle yourself
Most radiator valve leaks are at the spindle, and that one is a reasonable job to try before calling anyone. You need an adjustable spanner and a towel.
- Heating off and cooled down. Hot heating water under pressure is not something to be working next to.
- Take the head or cap off the valve. A thermostatic head usually unscrews or unclips at the collar. On a manual valve the cap pulls or unscrews off.
- Find the gland nut. It is the small nut the spindle passes through, directly under where the head was, not the larger nuts either side that join the valve to the pipes.
- A quarter turn clockwise, no more. Hold the valve body still with a second spanner if you have one, so you do not twist the pipe below it.
- Dry it, put kitchen roll under it, and run the heating. If the paper is dry after an hour hot, you are done. If it is still wet, a second quarter turn is fine. A third is not: the packing needs replacing, which is a job for someone with the parts.
If the leak is at either of the larger union or compression nuts, you can try a gentle nip in the same way, but stop at the first sign of the pipe moving. If the valve is on a pipe coming up through a wooden floor, the joint underneath may already be weakened. Our guide to radiator valve types and which ones weep explains why some valves leak far more often than others and when replacement is the better answer.
Leaking only when the heating is on, or only when it is off
That pattern helps. A valve that weeps only when the system is hot is usually a gland or olive that seals when cold and opens a fraction as the metal expands. A valve that weeps only when the heating is off, or only after it has been turned, is usually a gland that the spindle movement has disturbed. Both are the cheap end of the table above. Water that appears whether the system is hot or cold, and keeps coming with the valves shut, points at the pipe or the valve body.
What the repair involves
A gland or a union is a dry job: isolate, remake or repack, refill, rebalance the lockshield to the number of turns it was on, and check under load with the system hot. A valve replacement means isolating both ends where the valves will hold, or draining the circuit where they will not, cutting off the old tail if it is seized into the radiator, fitting a new valve and tail, refilling, venting, rebalancing and re-pressurising, then running the system to temperature and rechecking every joint cold and hot.
If the leak has been running a while, the floor matters more than the valve. Water at a valve drips onto one spot for weeks, and under carpet or engineered board it will have swollen the substrate and stained the joists. We lift, dry and reinstate rather than leaving you to find someone for the floor, which is the whole point of radiator and valve leak repair. Our rate for it is on the pricing page.
When it is not us
- A quarter turn on the gland nut stops it. Then it is done, and you did not need anyone. Snug, not forced: over-tightening a gland makes the valve stiff and shortens its life.
- Cold at the top, no leak. That is trapped air. Bleed it and top the system back up.
- The boiler is dropping pressure and nothing outside it is wet. That is a detection question rather than a valve question. Start at the boiler pressure hub.
- You rent. Report it to the landlord or agent in writing. Space heating installations are theirs to keep in repair, and they normally instruct their own contractor.
- Communal heating in a block. If the radiator is fed from a landlord's system, the managing agent controls who works on it and when it can be drained down.
- Anything inside the boiler case. Gas Safe registered engineers only. That applies whatever the fault looks like from outside.