Radiator leaking from the body (pinhole or seam)
Check the steps below first — if you're not confident, get it fixed safely today.
Post a job — we'll find you an engineer →⚠️ A radiator leaking from its body (as opposed to the valves or connections) cannot be permanently repaired — the radiator must be replaced. Do not use leak sealer products as these will contaminate the heating system and block the boiler heat exchanger.
A radiator weeping water through its panel is one of those problems that looks alarming but has a straightforward cause: internal corrosion. Over time, sludge and iron oxide build up inside the radiator, eating away at the metal from the inside until tiny pinholes or seam cracks develop. This typically affects older radiators or systems that haven't been properly maintained with inhibitor, and it's more common than you'd think—particularly in homes with hard water or systems that have never been flushed. The frustrating truth is that once this happens, there's no permanent fix short of replacement; no sealant product will stop it, and attempting to patch it will create far bigger problems down the line. This guide walks you through confirming what you're actually dealing with, how to manage it in the short term, and what to expect when you call a plumber to sort it properly.
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Most likely cause & what to check
Confirm the leak is from the radiator body and not a valve or connection — dry everything with a towel and observe carefully.
Pinhole leaks in radiator panels are caused by internal corrosion from sludge (iron oxide). They will get worse over time.
As a very short-term temporary measure, you can turn off the radiator by closing both valves — the TRV fully down and the lockshield valve. Place towels or a bowl to catch any remaining drips.
Do not use radiator leak sealant products — these are the same consistency as liquid gasket and will eventually block narrow passages in the boiler heat exchanger, causing a much more expensive repair.
Call a plumber to replace the radiator. A standard single-panel radiator costs £30–£100; labour is typically £80–£150/hour. The plumber will drain the circuit, remove the old radiator, and fit the new one.
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Frequently asked questions
Can I use radiator leak sealer to fix a pinhole leak?
No—leak sealers are a false economy. They're thick, gluey liquids that will eventually block the narrow pipes and channels in your boiler's heat exchanger, turning a £100 radiator replacement into a £1000+ boiler repair. It's not worth the risk.
Why is my radiator leaking from the body and not the valves?
Body leaks are caused by internal corrosion from sludge and iron oxide accumulating inside the radiator over years. Valve leaks are different—they're usually compression fittings or seals that can sometimes be tightened or replaced. A careful inspection with a dry towel will show you exactly where the water is coming from.
Is a leaking radiator dangerous?
It's not an immediate safety hazard, but it will cause water damage to your walls, floors, and furnishings if left unchecked. More importantly, you're losing heating system water, which will eventually affect pressure and efficiency. Shut it off and arrange replacement sooner rather than later.
How much does it cost to replace a leaking radiator?
A standard single-panel radiator costs between £30 and £100 from a plumber's merchant, with labour typically running £80–£150 per hour. The whole job—drain, remove, fit, and refill—usually takes 2–3 hours, so budget around £200–£350 in total for a straightforward replacement.
Can I just turn off the radiator and leave it?
As a temporary measure, yes—close both the TRV and the lockshield valve fully, place towels underneath, and it won't leak. However, this is a short-term holding pattern only. The radiator is corroding internally, and the leak will eventually worsen. You'll need to replace it to restore full heating to that room.
Will replacing my radiator prevent this happening again?
A new radiator will fix the immediate problem, but the real cause is sludge in your system. Ask your plumber about adding inhibitor to your heating water—it's inexpensive and will protect your new radiator and boiler from the same corrosion. A power flush of the system may also be worthwhile if sludge is widespread.