The fastest way to work out what’s wrong is to find exactly where the water is coming from. That also tells you whether it’s a DIY fix or a job for a plumber. A leak from a valve or a pipe joint is often a straightforward tightening job. A leak from the radiator’s body itself, though, is corrosion. Because of that, no amount of tightening will ever fix it.
Radiators only leak from a handful of places. Each one points to a different cause and a different level of urgency. Since guessing wastes time you don’t need to lose, spend a minute tracing the water back to its source before you reach for a spanner. Dry the area off with a cloth, then watch closely to see where it reappears.
Where is it leaking from?
There are only four places a radiator typically leaks from, and where you find the water tells you most of what you need to know.
Leaking from a valve (the wheel/lockshield at either end) — This is one of the more common leak points, and often one of the easier to deal with. It’s usually a loose nut where the valve meets the radiator. Or it’s a worn valve gland where the spindle passes through the valve body. A loose nut can sometimes be gently tightened, while a worn gland usually needs repacking, or the valve replacing if that doesn’t stop it.
Leaking from a pipe joint underneath — Check the compression fitting where the pipework meets the valve. These joints can work loose over time, especially after nearby work on the floor. A gentle tightening with the right spanner sometimes solves it. Be careful, though — overtightening a compression fitting can crack it or damage the olive inside. As a result, the leak gets worse rather than better.
Leaking from the radiator body itself (a pinhole or seam) — Water from a small hole in the flat panel, or along a welded seam, means corrosion. It’s working through the metal from the inside out. This isn’t repairable, because patching or sealing a pinhole is at best a short delay. The radiator will need replacing.
Leaking from the bleed valve at the top — A drip from the small bleed valve, usually in the top corner, is often just a loose bleed screw. Or its washer has perished. Tightening the screw with the correct bleed key, or replacing the washer, usually sorts it.
What you can safely try yourself
Once you’ve identified where the leak is coming from, there’s a short list of things worth trying first:
- Gently tighten a valve nut or the bleed screw using the correct spanner or bleed key — snug, not forced. Overtightening is one of the most common ways to turn a small leak into a bigger one.
- Put a container underneath to catch the drip and mop up around it while you assess the situation. That way, you’re not standing in water while you work out what’s wrong.
- If the leak looks like more than a minor weep, turn the valves off at both ends of the radiator — the wheel valve and the lockshield. This isolates it from the rest of the system while you decide what to do next.
That’s a good starting point, not a guarantee. It rules out the simplest causes and buys you time to assess things properly. It isn’t the same as saying every leaking radiator is a DIY job, though. Plenty aren’t.
When it needs a plumber
Get a plumber involved if any of the following apply:
- Tightening the valve or bleed screw doesn’t stop the leak, or it starts again within a day or two.
- The leak is coming from the radiator body itself. As covered above, that’s never a DIY fix — the radiator needs replacing, not repairing.
- You can’t identify where the water is actually coming from, even after drying the area and watching closely.
- Your system’s pressure keeps dropping and needs regular topping up, even if you can’t see an obvious leak anywhere. Frequent pressure drops like that usually mean there’s a leak somewhere in the system, seen or not, and it needs tracing properly, rather than guessing at it.
Frequently asked questions
Can I use a leak sealant additive instead of fixing it properly? Sealant additives poured into the system can sometimes slow a small pinhole leak for a while. They’re not a proper fix, though. They work by clogging the hole with fine particles. Those same particles can end up clogging valves, pumps, and narrow pipework elsewhere in the system. Treat it as a short-term stopgap at most. It’s not a substitute for fixing the actual cause.
Why does my boiler keep losing pressure if only one radiator is leaking? A slow radiator leak is one of the most common reasons a sealed system keeps losing pressure. Even a small, hard-to-spot drip adds up over several days. You might not notice a puddle if it evaporates, or soaks into carpet or floorboards, before it pools. If you’re regularly topping up the pressure, check every radiator, including underneath and behind, for damp patches or staining.
Is a leaking radiator an emergency? Usually not in the same way as a burst pipe. A radiator leak is typically a slow drip rather than a flood. So you’ve normally got time to assess it properly rather than panic. That said, it’s worth sorting promptly. Left alone, it will keep dropping your system pressure. Standing water under a radiator can also damage flooring and skirting boards over time.
Once you’ve traced the leak, our radiator & tap repairs page covers how we handle it in more detail. This includes when a gland just needs repacking, and when a radiator has reached the end of its life. Take a look at our pricing page to see how our pricing works, including our free call-outs, before you get in touch. Still not sure what you’re looking at? Reach out through our contact form. A couple of photos of where it’s leaking from helps us give you a straight answer. We cover radiator repairs in Chandler’s Ford, Hythe plumbing emergencies and Gosport call-outs. If it’s the boiler itself leaking rather than a radiator, see our boiler leak guide. If your water bill has jumped too, our high water bill checklist covers the other usual causes.