Heating 3 October 2026

Radiator Leaking at the Valve? Where the Drip Is Coming From and What to Do

A radiator leaking at the valve is almost always one of three things: a loose or worn gland around the valve spindle, a tired compression joint where the pipe enters the valve, or a failed union nut between the valve and the radiator itself. Most of these are small, slow leaks that you can contain today with a towel and a bowl, and many are fixed in under an hour once an engineer knows exactly where the water is coming from.

Why is my radiator leaking at the valve?

Radiator valves have more joints than people realise, and each one fails in its own way. When we are called out to a leaking radiator across west and mid Kent, these are the causes we find, roughly in order of how often we see them:

• The spindle gland. Where the valve head or cap sits, the spindle passes through a small packing gland. Over the years that packing dries out and water weeps up the spindle, especially just after the heating has been turned on for the first time in autumn.
• The union nut. This is the large nut joining the valve to the radiator tail. It can work loose as the radiator expands and contracts, and the olive or washer inside can wear.
• The compression joint. Where the copper pipe from the floor goes into the bottom of the valve there is a smaller nut and a brass olive. If the pipe was disturbed (by new flooring, a moved radiator, or a knock from the hoover) the seal can start to weep.
• The radiator tail. The threaded tail screwed into the radiator is sealed with PTFE tape or a sealing compound. When that seal fails the leak appears right where the valve meets the radiator.
• A corroded valve body. On older systems we sometimes find valves that are simply worn out, with pitting or a hairline crack. Those cannot be tightened and need replacing.

The first cold weeks of the season are when most of these show up. A valve that sat untouched all summer is suddenly asked to deal with hot water and expansion again, and old seals that were just about holding give way. It is the same reason so many radiator valves stick over the summer.

How to find exactly where the leak is

Before you touch anything, dry the whole valve and the pipe around it with kitchen roll. Then wrap a single dry sheet around each joint in turn and wait a few minutes. The sheet that gets damp first tells you where the water is coming from.

As a guide:

• Wet at the top of the valve, around the cap or head: the spindle gland.
• Wet at the big nut between the valve and the radiator: the union nut or the radiator tail.
• Wet at the small nut at the bottom where the pipe goes in: the compression joint on the pipe.
• Wet on the valve body itself with no obvious joint: a corroded or cracked valve.

Radiator leaking from the valve at the bottom

A drip that collects underneath the valve often looks like a bottom leak, but in our experience it is usually the union nut or the spindle above, with water running down the outside of the valve. Do the kitchen roll test before assuming the pipe joint is to blame.

Radiator leaking from the top or the bleed valve

If the water is at the top corner rather than at a valve, it is more likely the bleed screw or the blanking plug on the opposite side. A bleed screw left slightly open after bleeding is the most common cause we find, and it is worth checking the screw is closed firmly. Our guide on how to bleed your radiators covers doing it without leaving a weep behind.

What you can safely do yourself

There are a few sensible steps any homeowner can take before calling anyone:

1. Contain the water. A towel around the valve and a shallow container underneath stops damage to floorboards and the ceiling below. If water is already coming through a ceiling, see our advice on water leaking from the ceiling.
2. Turn the radiator off at both valves. Close the thermostatic or wheelhead valve fully, then close the lockshield valve on the other side (it usually needs a spanner or the plastic cap pulled off). Count the turns as you close the lockshield so it can be set back to the same position afterwards and the system stays balanced.
3. Try a gentle nip on the spindle gland. If the leak is clearly at the spindle, a small quarter-turn of the gland nut just under the head will often stop a weep. Go gently: brass is soft and an overtightened nut makes things worse.
4. Check the boiler pressure. A leaking radiator lets water out of a sealed system, so the pressure gauge on the boiler will drop. Our post on boiler pressure explains what the gauge should show, and if it keeps falling after the leak is fixed, why your boiler keeps losing pressure is worth a read.

What we would not recommend is reaching for a big spanner and cranking down on the union nut or the compression joint. On an older valve that can split the olive or crack the body, turning a slow drip into a steady flow. Leak sealers poured into the system are not a fix for a leaking valve either, and can gum up the boiler.

When the valve needs replacing

Some leaks are a five-minute job. Others mean the valve has to come off. We usually recommend replacing the valve when:

• the body is corroded, pitted or cracked
• the gland has been tightened before and is weeping again
• the valve is seized as well as leaking
• the tail seal has failed and the valve is old enough that it is worth renewing both together

Replacing a valve means draining the system down at least partly, swapping the valve and tail, then refilling, bleeding and re-pressurising. To see what is involved, read our guide on how to drain a central heating system.

If the water from the radiator is black, that is magnetite sludge, which wears valves faster. Where it is bad, a power flush can be the sensible longer-term answer.

Is a leaking radiator valve an emergency?

Usually not. A slow weep that you have contained with a towel and a bowl can wait for a booked visit. It becomes urgent when:

• the water is coming out faster than a steady drip
• it is reaching electrics, or coming through a ceiling
• you cannot isolate the radiator because the valves will not turn

In those cases, turn the heating off, isolate the radiator if you can and call our emergency plumbers. If the boiler pressure has dropped to nothing, the boiler will lock itself out, which is it protecting itself rather than a second fault. Anything involving the boiler itself or its gas supply must be handled by a Gas Safe registered engineer.

What does it cost to fix a leaking radiator valve?

We charge by the hour rather than a fixed price per job, so you only pay for the time it actually takes. The first hour is £95+VAT and each 30 minutes after that is £47.50+VAT, with parts on top. Most leaking valve repairs, and many valve replacements, fall within that first hour. If we find something bigger once we are there, such as several failing valves or a badly sludged system, we will explain it and give you a free quote before going any further.

Get a leaking radiator sorted

If you have a radiator leaking at the valve anywhere across Tonbridge, Tunbridge Wells, Sevenoaks, Maidstone and the surrounding villages, our team can find the source and fix it properly. Call us on 01732 792 454, or see our plumbing services for everything else we cover. For heating problems beyond the radiators, our boiler repairs page explains how we work.