There are a few reasons a radiator might spring a leak. Corroded base? Faulty TRV? Loose valve? All fair game. But in this guide, we’re focusing on one pesky culprit in particular - the leaking lockshield valve.
Below, we’ll walk you through what a lockshield valve does, how to find the leak, and how to fix it (if you’re feeling handy).
Let’s crack on…
🔑 Key Takeaways:
A leaking lockshield valve usually stems from the packing nut, valve-to-radiator joint, or the pipework connection.
PTFE tape and a bit of DIY confidence can often stop the leak.
If it’s beyond you (or you’re just not in the mood), a plumber can sort it for £35–£195.
Worst case scenario? You may need to replace the radiator - £230–£320.
What is a Lockshield Valve?
The lockshield valve is the (usually white-capped) valve on the opposite end of your radiator to the on/off control.
It regulates how much hot water flows out of the radiator and helps balance your heating system.
You won’t usually adjust it, that’s why it has a cap, but if it’s leaking, you’ll need to get up close and personal.
Which Part of Your Lockshield Valve is Leaking?
A lockshield valve can leak from several spots:
The packing nut (top of the valve, under the white cap)
The valve-to-radiator joint
The pipe-to-valve connection
Here’s how to sniff out the source:
Turn off the heating and let the system cool completely.
Remove the white cap (you may need a screwdriver for older valves).
Dry the valve thoroughly with a towel.
Wrap kitchen roll or tissue around different parts of the valve and check which bit gets wet first.
If it looks like it’s leaking from below but the top of the valve is damp, suspect the packing nut - water can trickle down and pool lower down.
Once you’ve ID’d the leak location, you’re ready to fix it.
What will you need?
Note: If you are unsure about any aspect of fixing a lockshield valve leakage, hire a professional plumber.
In general, you will need at least some of the following materials:
Adjustable spanner
Pair of grips
Screwdriver
PTFE tape
Bucket and towel
Kitchen roll
Pipe freeze kit (if you’re working on live pipework)
A brave face (optional)
How to Fix a Leaking Lockshield Valve
Fixing a Leak at the Packing Nut
This is the most common issue - and thankfully, one of the easiest to sort.
Option 1: Tighten It
Start by gently tightening the packing nut with an adjustable spanner. Often, that’s enough.
Option 2: Repack It With PTFE Tape
If tightening didn’t stop the leak:
Turn off your heating and let the radiator cool.
Unscrew and remove the packing nut.
Twist 6–8 inches of PTFE tape into a string.
Wrap the tape around the exposed valve stem.
Use a bradawl or similar to gently pack the tape into the stem cavity.
Refit and tighten the nut.
Still leaking? You may need a thicker wrap of PTFE tape. Trial and error might be needed.
Option 3: Replace the Packing Nut
If all else fails, the packing nut may be shot.
Replace it with a new one - or call in a pro if you’re not confident.
Fixing a Leak Between the Valve and Radiator
Same idea, different connection point.
Option 1: Tighten the Union Nut
Hold the valve steady and tighten the nut that connects it to the radiator.
If the leak worsens, stop - you could be loosening another seal.
Option 2: Drain and Pack the Joint
Turn off the heating and close all radiator valves.
Place a bowl and towel under the joint and loosen the nut to drain the radiator.
Open the bleed valve to let air in and speed up draining.
If the olive at the joint end looks damaged, replace it.
If it looks OK, wrap it with PTFE tape.
Re-tighten the joint, holding the valve steady.
Hiring a Professional to Fix a Lockshield Valve Leak
If you are unsure how to undertake this working DIY or have no success in your DIY attempts, you can always hire a professional.
On average it costs somewhere between £30 and £60 per hour to have a professional plumber undertake a given task.
The typical cost of hiring a professional to fix a lockshield valve:
Fixing a leak at the packing nut - £35 to £195
Fixing a leak at the pipework to valve union nut - £35 to £195
Fixing a leak at the valve to the radiator union nut - £35 to £195
Replace a broken radiator - £230 to £320
Prices vary by region, with London and the southeast being priciest. Northern England, Scotland, and Northern Ireland tend to be more budget-friendly.
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