How to Fix a Leaking Radiator Valve: Full Guide

Last updated on December 28th, 2024

Most radiator leaks come from a radiator valve. If your radiator is leaking water from the panel, you will most likely need to replace the radiator.

I have been fitting and fixing radiators full-time for over a decade and have learned a lot along the way.

Where is the valve leaking from?

A leak on a radiator valve will be on one of the two connecting nuts or the gland nut.

Valve nut

A valve leaking from the nut is the most common and easiest to fix on a central heating system.

There are three nuts on most radiator valves:

• The side nut connecting the valve to the radiator
• The bottom nut connecting the valve to the heating system
• The packing gland nut on the top of the valve

A leak can come from any nut. The simplest solution to fix the leak is to tighten the nut (turn clockwise) with an adjustable spanner. If this doesn’t work, you should add some plumbing jointing compound to the threads on the leaky nut.

Here’s how:

1. Drain the heating system
2. Turn the leaky nut anti-clockwise with a spanner until it comes away from the valve
3. Add lots of plumbing jointing compound to the threads
4. Tighten the nut back onto the valve
5. Clean all the excess jointing compound off the valve
6. Refill the system and check for leaks

Gland nut

A leaking lockshield valve can be fixed easily when it’s leaking from the packing gland on the top of the valve. The gland nut can be tightened (turned clockwise) with a spanner. This will fix almost all leaks from the gland.

If the valve leaks after tightening it, you can try wrapping some PTFE tape around the threads inside.

Here’s how:

1. Drain the heating system
2. Remove the packing gland with an adjustable spanner
3. Wrap some PTFE tape around the threads
4. Refit the gland in the valve
5. Refill the system
6. Check for leaks

Radiator drain valve leaking

To fix a leaking radiator drain valve, you will need to replace the rubber washer seal inside in most cases. A drain valve can be part of a radiator valve or a separate fitting on its own. The washer typically gets damaged by over-tightening when closing the valve.

The rubber washers tend to get crushed or pushed into the valve and can be a nightmare to remove.

How to replace the washer on a drain valve:

1. Drain the heating system
2. Remove the head of the radiator drain valve with some water pump pliers
3. Remove the black rubber washer
4. Fit new washer
5. Refill the heating system
6. Check for leaks

You might need to replace the radiator drain valve.

Radiator valve tail leaking

A radiator valve tail leaking is usually caused by one of three reasons:

• Not having enough PTFE tape on the threads
• The tail is not screwed into the radiator enough
• Rusting on old radiators

The tail leaking is the worst leak to get on a radiator.

Here are three ways to fix a leaking valve tail:

• Tighten the tail with a spanner
• Replace the PTFE tape
• Replace the tail

Tighten the tail

You can sometimes fix the leaky tail by turning it clockwise with a spanner. This is only possible if it’s sticking out enough and you have enough space to get the spanner in to turn it.

Replacing the PTFE tape

1. Drain the heating system
2. Remove the radiator valve with a spanner
3. Remove the valve tail with a spanner
4. Clean the old PTFE tape off the tail
5. Wrap some new PTFE tape around the threads (at least 15 wraps)
6. Refit the tail and tighten with a spanner (make sure it’s very tight or it will leak, remove the tail and add more PTFE if it’s not tight)
7. Refit the radiator valve
8. Refill the system
9. Check for leaks

Replace the valve tail

Sometimes the tail needs to be replaced. If so you can follow the same steps above for replacing the PTFE tape.

Thermostatic radiator valve leak

If you have a leaking thermostatic radiator valve (TRV), and it’s coming from the pin at the top of the valve, you will probably have to replace the full valve. Sometimes you can replace the gland seal on certain TRVs (Danfoss and Drayton do some) but you’re better off replacing the valve most of the time.

If the leak is coming from around the brass gland nut that the pin is in, then you can try tightening it with a spanner by turning it clockwise. Failing that you can try adding some PTFE tape to the threads.

Here’s how:

1. Drain the heating system
2. Remove the packing gland with a spanner
3. Wrap some PTFE tape around the threads
4. Refit the gland in the valve
5. Refill the system
6. Check for leaks

A thermostatic radiator valve leaking water from the pin has to be replaced, but if you want a temporary fix, you could try turning the radiator off when it leaks, as this might help until you replace the valve. If it’s leaking from a nut on the bottom or side of the TRV, you should follow the valve nut process at the top of this post.

Radiator bleed valve leaking

A radiator bleed valve leaking will usually mean you need to fit a new bleed valve. If the bleed screw is sitting in a bigger nut, then you can try tightening the nut with an adjustable spanner. If that doesn’t work you should add some PTFE tape or jointing compound.

Here’s how:

1. Close both radiator valves (or drain the system)
2. Open the bleed screw with a bleed key to release the pressure and catch the water until it stops coming out
3. Remove the radiator bleed valve or screw (whichever is leaking)
4. Add some jointing compound or PTFE tape around the threads
5. Refit the bleed valve
6. Refill the radiator or heating system
7. Bleed the radiator
8. Check for leaks

Valve leaking only when turned off

If you have a radiator valve leaking when it’s turned off, you could try opening the valve slightly to see if it stops. You should follow the steps above for a leaking lockshield valve if this does not work. But, you might have to replace the valve.

In my experience, a radiator valve leaking when it’s turned off is usually on ancient valves that are worse for wear and should probably be replaced.

Conclusion

Fixing a radiator valve leak is usually easy with no need to remove the radiator. Once you have found exactly where the leak is coming from, it should be a case of tightening the nut.

Draining the system and adding jointing compound or PTFE tape is a lot harder but might need to be done. Failing that, replacing the leaking valve might be the only solution.

Feel free to ask any questions in the comments below, and I’ll do my best to help. If you found this post helpful, please consider sharing it.

FAQs

Is a leaking radiator valve an emergency?

No, a leaking radiator valve is not an emergency. It can cause damage to flooring, electrics, and possibly the rooms below the leak, but I have not seen an emergency come from a leaking valve in over a decade of plumbing.

Can a leaking radiator valve cause boiler pressure to drop?

Yes, a leaking valve will cause boiler pressure to drop. A leaking radiator is the most likely cause of a boiler pressure drop, so if your boiler keeps losing pressure after repressurising it, you should look for a leak on your heating system.