How to Stop a Leak in a Radiator: Easy Guide to Fix Quickly

That sinking feeling when you spot a puddle forming under a radiator is a familiar one for many homeowners. But a small leak doesn't have to spiral into a catastrophe. Your first moves in those initial few minutes are what separates a minor cleanup from a major repair bill for water-damaged floors.

Don't panic. The goal is simple: contain the mess and isolate the problem.

Your First Moves When a Radiator Starts Leaking

First, grab some old towels and a bucket or basin. Mop up what's on the floor with the towels and stick the bucket right under the drip. This simple action immediately protects your flooring and buys you time to sort the problem properly.

Isolate the Leaking Radiator

With the immediate drip contained, your next job is to cut off the water supply to that specific radiator. Every radiator has two valves connecting it to the central heating system, and you need to close both to stop the flow completely.

• The Thermostatic Radiator Valve (TRV): This is the larger valve, usually with numbers from 0 to 5. Turn this dial all the way clockwise until it stops, usually on '0' or a frost symbol (*).
• The Lockshield Valve: On the other side of the radiator, pop the plastic cap off the second valve. Using an adjustable spanner, gently turn the small spindle underneath clockwise as far as it will go.

Pro Tip: As you're turning the lockshield valve, count how many turns it takes. Jot that number down. It makes re-balancing your heating system much easier once the leak is fixed.

With both valves shut tight, the radiator is isolated. For a major leak where shutting off the radiator isn't enough, you might need to learn how to turn off your water mains to prevent widespread damage.

Finding the True Source of the Leak

Now that you've managed the immediate gush, it’s time to play detective. You must find out exactly where the water is coming from to know how to tackle it.

First, grab a dry cloth and give the entire radiator a thorough wipe-down, including the valves and pipes. Once it's dry, press a fresh piece of toilet tissue against each joint and connection. Tissue is brilliant for this because it’ll show up even the faintest trace of moisture instantly.

Common Leak Culprits

Radiator leaks almost always come from one of three places. Knowing where to look saves a lot of time and guesswork.

• The Radiator Valve: This is the most frequent offender. Leaks can spring from the main body of the valve, the large nut connecting it to the radiator, or the spindle right under the cap.
• Pipe Couplings: The joint where the pipe feeds into the valve is another classic weak spot, usually due to a failing internal seal called an "olive".
• The Radiator Body: This one is more serious. Water weeping from the main body, especially from tiny 'pinholes', is a bad sign of internal corrosion.

A leak from the large nut connecting the valve to the radiator usually just means a failed seal that needs tightening or replacing. On the other hand, water seeping from the main radiator panel is a massive red flag for corrosion. A patch-up job won't cut it for this problem.

Practical Fixes for Common Radiator Leaks

Now that you’ve pinpointed the source, it’s time to get your hands dirty. Many common radiator leaks are well within the grasp of a confident DIYer. Before you start, isolate the radiator by closing both valves and put plenty of towels and a bucket underneath.

Addressing a Leaky Valve Spindle

A slow drip from under the valve's cap is a very common issue. First, try gently tightening the gland nut – the small nut right below the control cap. Give it a tiny clockwise turn with an adjustable spanner, no more than a quarter of a turn. This often fixes it.

If that doesn't work, you'll need to create a new seal using PTFE tape.

1. Carefully unscrew the gland nut.
2. Twist a 20cm piece of PTFE tape into a thin string.
3. Wrap this string tightly around the valve spindle.
4. Screw the gland nut back on firmly, but don't overtighten.

Sealing a Weeping Pipe Coupling

If the leak comes from the large nut where the pipe joins the valve, you’ll need to drain the radiator first. Undo the large union nut, slide it back, and you'll see a small metal ring called an "olive." This is what creates the watertight seal. Wrap the olive and the male threads of the valve with 10-15 layers of PTFE tape. Reconnect everything and tighten the nut securely with your spanner.

A Temporary Fix for Pinhole Leaks

A weeping spot on the radiator body is a sure sign of internal corrosion. The only long-term solution is a replacement, but you can apply a temporary patch with a two-part epoxy putty for plumbing. Drain the radiator, clean and scuff the area around the pinhole, and then press the mixed putty firmly over the leak. Let it cure fully before refilling. Remember, this is not a permanent solution.

Knowing When to Call a Professional Plumber

While DIY fixes are satisfying, knowing when to call a professional can save you from flooding and costly damage. If your best attempts fail, or if you patch one pinhole leak only to find another appearing, it's time for an expert. This indicates advanced internal corrosion, and a replacement is your only real option.

Red Flags That Demand an Expert

Certain situations require professional help. Attempting to fix these can lead to significant water damage:

• Leaks from Pipework in Walls or Floors: Never try to access hidden pipes.
• System-Wide Pressure Problems: If your boiler frequently loses pressure, a professional is needed to trace the leak.
• Visible, Heavy Corrosion: If the radiator or valves are heavily rusted, leave them alone. Applying force could cause a major failure.

When you're faced with a leak that's beyond a simple fix, or if you just want the peace of mind that comes with a professional job, don't hesitate. For reliable, expert help, our certified engineers are specialists in all manner of radiator repairs and are just a call away.

Proactive Steps To Prevent Future Radiator Leaks

Preventing a leak is better than fixing one. A few simple, regular habits can make a huge difference to the lifespan of your radiators.

The Importance Of Bleeding Your Radiators

Trapped air in your system creates pockets where oxygen and water can mix, causing rust from the inside out. Bleeding your radiators at least once a year releases this air, preventing corrosion and improving efficiency. It’s a simple job that makes a massive difference. For a detailed walkthrough, see our guide on how to bleed a radiator correctly.

Add a Central Heating Inhibitor

Central heating inhibitor is a chemical additive that protects the inside of your pipes and radiators. It creates a film on internal metal surfaces that stops rust and the formation of sludge, which is the number one cause of blockages and corrosion. Keeping the inhibitor level correct is your best line of defence against expensive repairs.

When a DIY job isn’t cutting it, or you simply want the reassurance of a professional, guaranteed repair, Go Assist is here to help. Our network of vetted, qualified engineers can sort out any radiator problem, making sure your home stays warm, dry, and damage-free. Book your expert repair online in just a few minutes.