How to Fix a Leaking Radiator Valve (Step-by-Step)

Leaking radiator valves can be subtle to spot but create very conspicuous damage. 

If left, even a tiny drip can stain carpets, warp wooden floorboards, and ruin plasterwork.

Fortunately, most radiator leaks are straightforward to diagnose and fix yourself. 

Which fix you need depends on where the leak is coming from. Use the sections below to identify your leak type, then follow the relevant fix.

How to find the source of a radiator valve leak

A pool of water on the floor is usually easy to spot (depending on the type of flooring below). But finding exactly where it escaped from the pipework requires a systematic approach.

Turn your heating off

Turn off your heating and allow the radiator to cool (i.e., until all radiators are cold to the touch) before you begin.

Inspecting pressurised valves when the system is still on puts you at risk of being burned.

Dry the entire radiator

Use a dry, absorbent cloth to wipe down the:

• Radiator body
• Valves
• Connecting pipework

This should enable you to more easily see which area the water is seeping out from.

Test with tissue paper

Pat a piece of dry tissue (or kitchen) paper around each connection joint, the main valve body, and the metal spindle. Look closely at the paper to see where damp patches form first. 

This should give you a more precise idea of which joint is weeping.

Is a leaking radiator valve an emergency?

If your radiator valve is only releasing small and infrequent drops of water, it’s not an emergency. You still have time to carry out a DIY repair.

But you should never ignore a leak. Over time, even a small dripping leak will cause serious damage.

And if the leak is a steady, continuous stream, you must isolate your heating system immediately to prevent flooding.

Why is my radiator valve leaking?

Once you’ve found the source, use this to identify which fix applies:

• A loose union nut: The union nut is the large brass nut that connects the radiator valve to the radiator itself. If it’s loose, water will slowly weep past the connection. → Go to Fix 1
• A damaged spindle packing: The spindle is the metal pin inside the valve that moves when you turn the handle. If the internal packing wears out, water can leak out around the spindle, especially when the valve is left partly open. → Go to Fix 2
• A worn valve body: If the brass body of the valve is cracked, heavily corroded, or covered in mineral scale, there is no DIY fix. You will need to replace the entire valve.

Fix 1: How to reseal a loose union nut

The union nut is the large brass nut that joins the valve body to the copper pipework. 

It sits just below the valve itself and can be loosened or tightened with a spanner. If water is weeping from this connection, you can reseal it using PTFE (polytetrafluoroethylene) tape. 

This applies to both the control valve (manual or TRV) and the lockshield valve

What you will need

• An adjustable spanner
• A radiator bleed key
• A roll of PTFE tape
• A bucket or container (washing up bowl, jug, etc.)
• Old towels or cloths

Step 1: Protect your floors

Cover the floor surrounding the radiator with old towels and place your bucket directly under the leaking valve to catch any water that escapes.

Step 2: Close the radiator valves

Go to each side of the radiator and turn both valves fully clockwise.

For the manual valve or TRV, turn the handle until it stops. 

For the lockshield valve on the opposite side, remove the plastic cap and use your adjustable spanner to turn the metal spindle clockwise until it’s tight. 

Note down the exact number of turns so you can restore your radiator’s balance later.

Step 3: Open the radiator bleed valve

Insert your radiator bleed key into the valve at the top of the unit and turn it anti-clockwise. A small hiss of air may escape, but water should not stream out.

If it does, your valves are not fully closed and the radiator is still under pressure. So, close the bleed valve immediately before continuing.

Step 4: Loosen the union nut

Use your adjustable spanner to slowly loosen the union nut that connects the valve to the radiator.

Have your bucket ready, as water trapped inside the radiator body will begin to drain out. Slide the nut back to expose the copper pipe and the brass olive ring.

Step 5: Apply the PTFE tape

Wrap your PTFE tape tightly around the exposed pipework and the olive, clockwise, about 10–15 times to ensure a robust, watertight seal.

Step 6: Retighten the union nut

Slide the union nut back onto the pipe and tighten it by hand. Then use your spanner to secure it firmly. 

Take care not to over-tighten. If you’re too rough with it, you can crush the brass olive or split the joint, creating a worse leak that’s harder to repair.

Step 7: Turn the radiator back on

Turn the manual or TRV valve fully anti-clockwise. Then open the lockshield valve by the exact number of turns you noted down earlier.

Open the bleed valve at the top to let any trapped air escape. Close it tightly once a steady trickle of water appears. Wipe the valve dry and inspect it closely for any fresh signs of a leak.

Fix 2: How to repack a leaking gland (spindle leak)

If water is seeping from directly under the plastic handle or TRV head, the issue is likely a weeping packing gland surrounding the metal spindle. This fix does not require draining the system.

Remove the plastic cap or TRV head to expose the metal spindle and the small gland nut below it. 

Use your adjustable spanner to tighten this nut clockwise by about a quarter-turn. In many cases, this slight adjustment compresses the internal packing enough to stop the drip.

If it still leaks, turn your spanner anti-clockwise to loosen and slide the gland nut up the spindle.

Wrap a few turns of PTFE tape tightly around the exposed spindle, and use a flathead screwdriver to pack (/squash!) the tape down into the gland. 

Slide the nut back down and tighten it firmly. This creates a fresh, watertight seal around the moving spindle.

Fix 3: How to fix a leaking lockshield valve

The lockshield valve (the capped valve on the return side of the radiator) leaks for the same two reasons as the control valve:

• A loose union nut
• A worn gland. 

Apply Fix 1 or Fix 2 accordingly, with one extra step: 

• Remove the plastic cap before you begin, and use a spanner rather than a handle to close it.

When you reopen it, restore it to exactly the same number of turns as before to preserve your system’s balance.

Fix 4: How to fix a leaking TRV head

If water is weeping from the TRV head itself rather than from the valve body or union nut, the head is the problem. 

Unscrew the TRV head from the valve body (most twist off anti-clockwise). 

Check the O-ring seal at the base of the head. If it’s cracked or compressed flat, replace the O-ring (available from any plumbing merchant for under £1). 

If the head itself is faulty, replace the head only. You don’t need to drain the system or touch the valve body.

Fix 5: How to fix a leaking bleed valve

A weeping bleed valve usually just needs closing fully. 

Insert your bleed key and turn clockwise until it stops. If it still drips, the valve insert has worn out. 

You can replace the insert without draining the system: 

• Close both radiator valves
• Open the bleed valve to release pressure
• Unscrew the insert with a screwdriver
• Wrap the thread with PTFE tape
• Fit the new insert.

Why does my radiator valve leak when the heating is switched off?

A valve that leaks only when the heating is off — or immediately after it shuts down — usually indicates a worn valve seat or gland rather than a loose connection. 

As the system cools and pressure drops, a failing seal that held under pressure begins to weep. 

You can try to apply Fix 2 (gland repacking). But if the leak returns repeatedly, the valve body itself has worn out and needs replacing.

When the leak is coming from a pipe

If you discover your leak is coming from a pipe, not a valve, follow our instructions on what to do next.

When to call a professional

Most radiator valve leaks are within reach of a confident DIYer with basic tools. Call a heating engineer if:

• The leak is near an electrical fitting or consumer unit
• You cannot isolate the radiator (valves won’t close)
• The leak continues after completing the relevant fix above
• The valve body is visibly cracked or heavily corroded

A heating engineer will typically charge £50–£100 to replace a radiator valve including labour. The job usually takes under an hour. 

Replacement valves cost £10–£50 for a standard manual or TRV, or £40–£80 for a smart TRV head.

Get your central heating covered with Hometree

Our central heating cover includes unlimited repairs, an annual boiler service, zero parts & labour charges, and 24/7 claims support to keep your home warm. Subject to exclusions and T&Cs apply.

With no hidden fees and coverage across England, Scotland, and Wales, we’ve got you covered.

You can get covered today or contact us for a free quote.