How to Fix a Leaking Radiator

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8 min read|Updated: Jun 27, 2026|By Home Repair Expert

Quick Answer

A leaking radiator usually leaks from one of five points: the valve packing nut (tighten 1/4 turn), the valve body (replace the valve), the pipe joint (re-wrap PTFE tape), the radiator body (pinhole leak, use radiator sealant), or the bleed valve (replace the small bleed plug). Identify which before treating, because the wrong fix wastes time and water.

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A leaking radiator is a problem worth fixing fast. Even a slow drip can damage flooring, stain the wall, and eventually drop your heating system pressure, leaving your boiler unable to maintain heat. The reassuring news is that many radiator leaks are simple to identify and fix yourself with basic tools and the right precautions.

This guide walks you through finding where the leak is coming from and stopping it, whether the drip is at a valve, a union, or the body of the radiator itself.

Why Radiators Leak

A radiator leak almost always starts at one of a few common spots. Pinpointing the source decides the fix:

• A loose valve or union: The nut where the valve meets the pipe or the radiator can work loose and weep, the most common source of a small leak.
• A worn O-ring or gland: The seal around the valve spindle perishes and drips when the radiator is hot or the valve is operated.
• A failed valve: The valve body itself can corrode or fail and need replacing.
• Sludge corrosion in the radiator body: Internal sludge over many years can corrode the radiator from the inside and cause pinhole leaks, usually meaning the radiator needs replacing.
• A leak at the bleed valve: A loose or damaged bleed screw can drip after bleeding the radiator.

Tools and Materials You Will Need

• Towels and a bowl
• Adjustable wrench or radiator spanner
• Pliers
• PTFE (plumber’s) tape
• Replacement O-ring or valve (if needed)
• Bleed key
• Radiator leak sealer (as a temporary measure)

Step-by-Step: How to Fix a Leaking Radiator

Step 1: Find the Source of the Leak

Wipe the radiator and valves dry, then watch closely with a torch. Pinpoint whether the water appears at a valve nut, around the spindle, at the bleed screw, or from the radiator body itself, this tells you exactly what to fix.

Step 2: Tighten Loose Connections

For a drip at a valve nut, hold the valve body steady with one wrench and gently snug the connecting nut with another. Do not overtighten, just enough to stop the weep.

Step 3: Re-seal a Spindle Leak

A drip from around the valve spindle usually means a worn O-ring or gland packing. Drain the radiator, disassemble the valve head, fit a new O-ring, and wrap fresh PTFE tape around any threaded joints as you reassemble.

Step 4: Stop a Bleed Screw Leak

For a drip from the bleed valve, gently tighten it with a bleed key. If it still leaks, replace the bleed plug, an inexpensive part available at any hardware store.

Step 5: Address a Pinhole Leak

A leak from the radiator body itself usually points to internal corrosion. A radiator leak sealer added to the system can buy time, but a body leak typically means the radiator needs replacing, a job best handled by a heating engineer.

Pro Tips to Prevent This Problem

• Keep towels and a bowl handy whenever you open a heating connection; some water always escapes.
• Wrap PTFE tape clockwise around threads so it tightens rather than unravels.
• Bleed your radiators annually and consider a system inhibitor to slow internal corrosion.

When to Call a Professional

Call a heating engineer if the leak is from the body of the radiator (pinhole corrosion), if multiple radiators are leaking, or if you have a sealed pressurised system you are not confident draining. A failed radiator usually means replacement, and balancing or refilling the system afterward is best left to a professional.

Frequently Asked Questions

How do I find where my radiator is leaking from?

Dry the radiator and valves completely, then watch with a torch. Water that appears at a valve nut, around the spindle, at the bleed screw, or from the radiator body each indicates a different fix.

Can I stop a radiator leak temporarily?

For a small leak, a radiator leak sealer added to the system can buy time. However, body leaks from internal corrosion usually mean the radiator needs replacing, and a heating engineer is the right call.

Should I be worried if my radiator is leaking?

Even a small radiator leak is worth fixing promptly. It can damage flooring, drop your system pressure, and indicate internal corrosion that may worsen quickly if not addressed.

Final Thoughts

A leaking radiator is usually fixable without a plumber when the source is a loose union, a worn O-ring, or a bleed valve. Pinpoint the leak, snug the connection, replace seals with fresh PTFE tape on threads, and tackle a leaky bleed plug cheaply. Save the call to a heating engineer for body corrosion, multiple leaks, or sealed-system work, and you can keep your heating tight and your floors dry.