How To Fix A Radiator Leak

Is your radiator leaking? Don't panic; let's see if we can help and fix your leak.

We rely on our radiators to heat up year after year, but they’re far from indestructible. After many years of humble service, radiators often show signs of wear and tear, they can start making rattling noises, become cold or even start hissing!

Over time, a build-up of sludge and corrosion inside the radiator and plumbing might cause a leak. The same goes for the valves - if they wear out, they might start leaking. 

If your radiator is leaking, don’t panic! Before you do anything, shut your central heating off to ensure the water cools thoroughly. 

Get some towels at the ready - make sure the leaking water doesn’t seep into the floor or carpet!

Without further ado, here’s how to fix a leaking radiator. 

Why does a radiator leak?

Cleaning up a leaking radiator
Above: Leaking Radiator

Radiators often leak due to worn valves or tiny holes in the radiator itself. To fix a leak, you need to find out where it’s coming from first (if you don’t already!)

Leaks typically originate from one of four areas:

  1. The radiator’s main metal body. 
  2. The bleed valve.
  3. The TRV or lockshield valves
  4. The plumbing going in or out of the radiator. 

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Tiny leaks in the radiator and pipework are called pinhole leaks. The TRV valve and lockshield valves may also leak if you use them often, as the spindle will become worn over time. 

White radiator TRV valve
Above: TRV Valve

Most leaks are small, and you might not even realise until you discover a wet patch on the floor. 

Rarely, leaks might cause water to build up in floorboards, leaking through to the next floor and rupturing paintwork. Leaks in the pipework are generally harder to detect - look for new watermarks or damp spots on your walls and ceilings. 

How to find a radiator leak

Firstly, make sure your radiators are totally dry - wipe them down with a cloth. Then, shut your central heating off and turn it on again to get the water flowing to your radiators. 

Then, locate the suspected leaking radiator and watch carefully for any trickle of water over the radiator body or valve. The pipes leading to and from the radiator may also be leaking. 

By taking a small piece of toilet paper and padding that over the dry radiator, you can locate the leak by seeing if and when the toilet paper becomes wet. 

The leak is coming from the bleed valve

The bleed valve should be tight to prevent water from escaping. If it’s leaking, simply tighten it up with a bleed key. 

Bleeding radiator into a mug
Above: Bleed Valve

Possible Radiator Leaks and how to fix them

1: Leaking from radiator body: pinhole leaks

Pinhole leaks from the radiator body are usually caused by internal corrosion. While it’s possible to fix small leaks from the exterior using epoxy putty, corrosion might become an ongoing problem that eventually necessitates replacing the entire radiator.

How to fix a pinhole leak

Individual leaks are fixable with epoxy putty. You’ll need to isolate your radiator and drain it to below the level of the leak. Make sure the radiator is completely clean and dry before applying the putty. 

If your radiators and plumbing are suffering from multiple pinhole leaks, introducing a leak sealer to the system is a good idea. 

This is pretty easy to do for open vented systems - simply follow the guidance of the product to introduce it into an almost-empty feeder tank (typically located in the loft). 

If you have more than one pinhole leak, these should be considered temporary fixes. Old plumbing systems might be full of corrosive sludge and will benefit from a powerflush or the systematic replacement of older pipework and radiators. 

2: Leaking radiator valve

Leaking TRV valves are common, especially if you adjust their settings often. 

If you notice water leaking from the TRV valve: 

  • Turn the valve off and remove the cap. 
  • Under the cap, you’ll see a large nut called the gland nut. The leak will likely emanate from underneath this nut. 
  • Turn off the lockshield valve before altering anything, and prepare for water to leak from the spindle. 

How to fix a leaking radiator valve

You can try simply tightening the gland nut up if it’s loose - this might solve the issue. 

Otherwise, you’ll need to grab some PTFE plumbing tape, unscrew the nut, wrap some lengths of the tape around the thread (probably around 5 to 15 lengths), and tighten up the nut. 

Yellow and white PTFE Tape
Above: PTFE Tape

Then, pack the tape into the spindle using a screwdriver. Remember, turn your heating off and turn the valve off prior to doing this!

3: Radiator spindle leak

If your TRV valve is leaking, the leak is likely originating from the spindle. Rarely, it may originate from the coupling located on pipes adjacent to the valve. 

The likely culprit is a metal sleeve called the olive. Replacing the olive might do the trick if the above steps don’t work, but if not, it’s worth replacing the entire TRV valve. 

Older TRVs are prone to wear and tear, and while PTFE tape is effective for repairing a leaking spindle, it’s still a temporary fix. 

How to fix a radiator spindle leak

To fix a TRV valve spindle leak, try tightening the gland nut. If that fails, wrap some PTFE tape around the thread under the gland nut and re-tighten the nut. 

If the valve continues to leak, it’s sensible to consider replacing the entire thing. TRV valves aren’t expensive, and new models are typically very durable and long-lasting. 

4: Radiator pipe joint leak

If your leak is emanating from a pipe or pipe joint, you can repair small pinhole leaks with either epoxy repair putty or a pipe sleeve. First, you’ll need to turn off your water supply and isolate the pipe to relieve water pressure from the leak. 

How to fix a radiator pipe joint leak

Epoxy putty and pipe sleeves are relatively simple to apply. However, the pipe needs to be clean and dry prior to application. 

The most complex part is draining and refilling the system - book an appointment with one of our expert engineers.

Summary: How to fix a leaking radiator

Many radiator leaks are easy to find and fix. TRV valves are often the culprit, but pinhole leaks can originate from the pipework or body of the radiator itself. 

One or two pinhole leaks are easily repairable using a combination of epoxy putty and/or pipe sleeves. You can also buy leak sealers that you ‘pour in’ to the system - these are effective for fixing obscured pinhole leaks in radiators and piping. 

As ever, if you’re unsure, get in touch with us today.

Read our other guides on radiators

Fix your cold Radiator
Fix your hissing Radiator
Fix your noisy boiler
Most common towel radiator problems
Fix your rattling radiator

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