At a glance
A leaking radiator is one of the most common home maintenance issues in UK homes and in most cases it is a job that a competent DIYer can handle without calling a plumber. The key is identifying where the leak is actually coming from before reaching for any tools – a puddle on the floor beneath a radiator could be caused by a loose valve gland nut, a corroded bleed screw, a failing pipe joint or, less commonly, a pinhole in the radiator body itself. Each has a different fix and different implications for whether professional help is needed.
The good news is that the majority of radiator leaks in UK homes are external – at valve connections, bleed points or pipe fittings – and are straightforwardly repaired with basic tools and a few pounds of materials. Internal leaks from a corroded radiator body are less common but require replacement rather than repair. This guide works through the diagnosis process and covers the standard repairs for the most frequent causes of leaking radiators in UK central heating systems.
What you’ll need
Diagnosing where the leak is
Before doing anything else, dry the area around the radiator completely with a towel and then run the heating for 30 minutes to bring the system up to temperature. Watch carefully where moisture reappears – a slow drip from a specific point tells you exactly where to focus. The most common leak locations on a UK radiator are the valve gland (where the spindle enters the valve body), the valve tail connection (where the valve connects to the pipe), the bleed screw at the top of the radiator, and the pipe fittings where the flow and return pipes connect to the radiator valves. If moisture appears across a wider area rather than from a single point, use dry tissue paper pressed against each fitting in turn to identify the precise source – the tissue will show exactly where water is tracking from.
Once you have identified the leak location, dry the area again and test whether the leak is from the valve spindle/gland area (at the top of the valve where the control knob sits), from the compression fitting at the base of the valve where it joins the pipe, or from the bleed point at the top of the radiator. Understanding which of these three areas is affected determines the repair approach. A leak from the spindle is usually fixed by tightening the gland nut. A leak from a compression fitting may need the joint repacking or retightening. A leaking bleed screw is usually the simplest fix of all.
Turn off the heating and let it cool before working on any valve. Central heating water runs at 70-80 degrees Celsius under pressure. Always allow the system to cool completely before undoing any fittings. Isolate the boiler and confirm the water is cool before beginning any repair work.
Fixing a leaking valve
The most common radiator valve leak in UK homes is from the gland nut – the nut that compresses packing around the spindle to create a water-tight seal. Over time this packing compresses and the seal fails. The repair is straightforward: first attempt to tighten the gland nut by a quarter turn with an adjustable spanner while the heating is off and the system cool. In many cases this is enough to stop the leak. If tightening does not resolve it, the packing needs replacing.
To repack a valve gland, close both valves on the radiator (turn the TRV to off and the lockshield fully clockwise), then place towels under the valve and have a container ready. Using an adjustable spanner, carefully undo the gland nut – water will seep out as you do so, hence the towels. Wrap PTFE tape around the spindle several times to form new packing, then retighten the gland nut firmly. Turn the valves back on, refill the system if needed and check for leaks once the heating reaches temperature. If the gland nut is corroded or damaged, or if the valve body itself shows signs of significant corrosion at the spindle housing, replacing the entire valve is the better long-term solution rather than repeatedly repacking a failing gland. Replacement TRV valves and lockshield valves are available from plumbers merchants and DIY stores for £15-30, and the fitting process is the same as repack work except the valve body is also removed and replaced.
Fixing a leaking bleed point
A leaking bleed screw is one of the simplest radiator repairs. The bleed screw sits at the top corner of the radiator and is opened with a radiator key to release trapped air. Over time the small rubber washer inside the bleed point degrades and allows water to seep past. With the heating off and the system cool, use the radiator key to ensure the bleed screw is fully closed – clockwise until firm but not overtightened. If the screw is closed but still drips, the screw needs replacing.
Replacing a bleed screw requires isolating the radiator by closing both valves and placing towels to catch the small amount of water that drips as the screw is removed. Use the radiator key to unscrew the old bleed screw completely, fit the replacement – which should come with a new washer – and tighten firmly with the key. Turn the valves back on and bleed the radiator in the normal way once the system refills, checking that the new screw does not seep when fully closed.
Add inhibitor when you refill. Any time you drain down or partially drain a radiator, the system loses some of the inhibitor chemical that protects the pipework from corrosion. Add a suitable central heating inhibitor to the feed and expansion tank or through the filling loop when refilling. A bottle costs around £10 and protects the system from the sludge build-up that causes cold spots and long-term boiler problems.
When to call a plumber
There are circumstances where a leaking radiator is beyond a straightforward DIY fix and calling a qualified plumber is the right decision. A leak from the radiator body itself – where rust staining or moisture appears on the flat panel face rather than at any fitting – indicates internal corrosion and the radiator will need to be drained and replaced. This is a job that requires isolating that section of the circuit, removing the radiator and fitting a new one, which involves compression fittings on copper pipe and is within the scope of an experienced DIYer but beyond most beginners.
If the leak is from the boiler itself or from pipework that is not directly at the radiator – under floorboards, behind walls or at the main feed and expansion tank – this is beyond DIY territory and a Gas Safe or qualified plumber should be contacted. A boiler that is dripping or losing pressure repeatedly without any visible external leak may have an internal seal failure, which requires a qualified engineer to diagnose and repair. Similarly, a system that repeatedly loses pressure even after topping up suggests a leak somewhere in the circuit that has not yet been located.
If your boiler is losing pressure regularly, addressing it promptly protects both the boiler and the wider heating system from the accelerated corrosion that low-water operation causes. Once any leak repair is complete, re-check that the system pressure is correct on the boiler gauge – most UK combi boilers operate between 1 and 1.5 bar when cold – and top up via the filling loop if needed. If the radiator has been partially drained during the repair, you will also need to bleed it once the system refills and reaches temperature to remove any air that entered. Our guide to how to bleed a radiator covers the process in full, including the sequence for bleeding multiple radiators across a full system. For homes that also have a leaking shower or other plumbing issues, addressing these at the same time as a heating repair reduces the number of times the water supply needs to be isolated.
Share on socials:
