Radiator leaking from the valve, a pipe joint or the radiator itself? How to find the leak, contain it safely and when you need a plumber in Edinburgh.
By AJ, certified Gas Safe engineer and lead plumber at 247 Emergency Plumbers Edinburgh · Checked
Most radiator leaks come from the valve, the spindle under the valve cap, a pipe joint or a pinhole in the radiator body. Dry the radiator and wipe each area with tissue to find the wet spot. Small valve and spindle leaks can sometimes be stopped by gently tightening a nut. A pinhole in the radiator itself usually means the radiator needs replacing.
Quick guide: cold at the top means air (bleed it). Cold at the bottom means sludge (needs flushing). Cold all over while others are hot usually means a stuck valve.
What it could be and what to do
Valve or spindle leak You may be able to fix this
Likely cause: HomeServe says valve leaks usually come from the coupling nut, the olive inside it or worn spindle packing. Water seeping from under the valve cap points to the spindle.
What to do: Put a towel and container under it. Try a gentle quarter turn on the gland nut under the cap. If it still drips, the valve needs repacking or replacing: call a plumber.
Pipe joint leak You may be able to fix this
Likely cause: The joints where the pipes meet the radiator valves can loosen over time.
What to do: Tighten the nut slightly with a spanner while holding the valve still with another. If it keeps leaking, it needs draining and resealing by a plumber.
Pinhole in the radiator Engineer needed
Likely cause: Corrosion inside the radiator, often from sludge or air in the system, eats through the metal and leaves a small hole.
What to do: Close both valves to isolate the radiator: turn the TRV to off and the lockshield clockwise, counting the turns. On a sealed system (most combi and system boilers), the main stopcock will not stop this leak. Then call us: the radiator usually needs replacing.
Leak with a pressure drop Engineer needed
Likely cause: Every leak lets water out of the heating system, so the boiler pressure falls and the boiler may stop.
What to do: Watch the boiler gauge. Do not keep topping up a leaking system: fix the leak first, then repressurise to about 1 to 1.5 bar.
Safe radiator checks you can do
These are the checks we suggest without an engineer. Never open the boiler casing.
Heating off first: turn the heating off and let radiators cool before you bleed them or touch a valve. The water can scald.
Feel the radiator: with the heating on, note whether it is cold at the top, the bottom or all over. That tells you which page above to use.
Valves open: check the thermostatic valve is turned up and the lockshield at the other end is not closed.
Bleed: open the bleed valve slightly with a radiator key, catch the water and close it when water flows steadily.
Pressure: after bleeding, check the boiler gauge shows about 1 to 1.5 bar when cold, and top up as your manual shows. Low boiler pressure guide →
Radiator still cold or leaking? We can sort it.
Our callout is from £75 in standard hours (out of hours £100–£180) for attendance and diagnosis. Repair labour and any parts are agreed with you before work starts.
Our emergency line is open 24 hours a day, 7 days a week.
Every heating system is different. This page is general guidance, not a diagnosis.
YOUR QUESTIONS, ANSWERED
Helpful answers before you call.
What should I do if my radiator is leaking?
Catch the water with a towel and container, find where it is coming from, and close both radiator valves if it will not stop. Turn the TRV to off and the lockshield clockwise. Then call a plumber. In Edinburgh, call 0131 210 0505.
Will turning off the stopcock stop a radiator leak?
Usually not. Most homes with a combi or system boiler have a sealed heating system, which is separate from the cold mains. Closing the two valves on the radiator isolates it instead.
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