Glossary · Central heating, radiators and hot water
What should I do about a leaking radiator valve?
A leaking radiator valve is a valve or pipe connection at a radiator that lets heating water escape. Vaillant names radiator valves as one of the most common places for a heating system to leak. The signs are damp patches, stains or a boiler that keeps losing pressure. It needs a competent person to repair.
Key points
- Vaillant says radiator valves and system components are the most common places for a heating leak, and that leaks lose boiler pressure.
- Look for damp patches, flaking paint, skirting board damage or stains on the floor or ceiling below.
- Ideal Heating says slow leaks can evaporate before they form puddles, so check for clean spots in dust or dark marks.
- Vaillant says not to repair loose or broken pipework joints unless you are trained to do so.
- Ideal Heating says fixing a leaking water pipe is usually a job any plumber can do. A leak from the boiler itself is different.
What causes it
The circuit of pipes and radiators connected to a boiler can corrode or loosen over time. Vaillant says this eventually lets water escape, and the boiler pressure gradually drops as the water is replaced with air. It names radiator valves and other system components as the most common places for a leak.[1]Vaillant, Why is my boiler losing pressure?
Radiators have a thermostatic or manual valve at one end and a lockshield valve at the other, and each has pipe connections. Glow-worm describes the valves at the bottom of a radiator, which is where the connections are.[4]Glow-worm, Why is my radiator cold at the bottom?
What you can check yourself
Finding the leak is the part a householder can do. Vaillant says it will most likely be around the connections on radiators. Look for damp patches, discoloured paint or flaking on the pipework and skirting boards, and water stains on the floor or ceiling. Pipework can look wet from condensation, so wipe it clean and put a plate underneath to see if it drips.[1]Vaillant, Why is my boiler losing pressure?
Ideal Heating says to check around the radiators where the pipework enters and leaves, and warns that slow leaks can evaporate before they form puddles. It suggests looking for clean spots on hard floors surrounded by dust, black marks where dampness has taken hold and stains on ceilings.[2]Ideal Heating, Why is my boiler losing pressure?
A leak also shows on the boiler gauge. Vaillant says a reading below 1 bar means the boiler has lost pressure.[1]Vaillant, Why is my boiler losing pressure? Ideal Heating says it is usually easy to top up using the filling loop, but that a boiler that has lost pressure usually has a cause, so topping up may only be a temporary measure.[2]Ideal Heating, Why is my boiler losing pressure? See low water pressure.
What to do and who fixes it
Vaillant says not to attempt to repair loose or broken pipework joints unless you are trained to do so, and to arrange for a specialist to make the repair and then check the boiler stops losing pressure.[1]Vaillant, Why is my boiler losing pressure? Ideal Heating says that if there is standing water you should call a plumber, and that fixing a water pipe is usually a job any plumber can do.[2]Ideal Heating, Why is my boiler losing pressure?[3]Ideal Heating, My boiler is leaking: what should I do?
When a radiator is worked on, Glow-worm says the installer lays sheets under it to protect the floor, closes the valves so it does not refill when drained, and lets the radiator cool first.[4]Glow-worm, Why is my radiator cold at the bottom? If the leak is from the boiler itself, that needs a Gas Safe registered engineer. See boiler leaking water.
Example
Jasmine in Leeds notices her boiler pressure has dropped below 1 bar three times this month. She tops it up each time. She then wipes the pipe joint under the bedroom radiator and sees a bead of water on the carpet. She stops topping up and asks a plumber to look at the valve rather than trying to tighten it herself.
What people get wrong
Many people top up the pressure each time and carry on. That hides the leak but does not remove it, and the damp can damage floors and ceilings. A radiator valve that weeps is a sign that something needs repair.
Topping up with plain water repeatedly can also dilute the corrosion inhibitor. Ideal Heating says the concentration may then become too low and a specialist should drain and refill the system with the correct amount.[2]Ideal Heating, Why is my boiler losing pressure?
The bottom line
A leaking radiator valve is one of the most common causes of a heating system losing pressure. You can find the leak, wipe it, put a bowl under it and keep an eye on the gauge. The repair belongs to a plumber or heating engineer, and the boiler stays a Gas Safe job.
Common questions
How do I find a leak in my heating system?
Vaillant says it is most likely to be around the connections on radiators. Look for damp patches, discoloured or flaking paint and water stains on skirting, floors or ceilings. Wipe pipework dry and put a plate underneath, because condensation can look like a leak.
Does a leaking radiator valve make my boiler lose pressure?
Yes. Vaillant says a leak from the system, most commonly at radiator valves, lets water escape and the pressure gradually drop as air replaces it. Ideal Heating says central heating leaks are rarely torrential but lower pressure over time.
Can I just tighten it?
Vaillant says not to attempt to repair loose or broken pipework joints unless you are trained to do so, and to arrange for a specialist to make repairs. Ask a plumber or heating engineer to look at it.
Is it a gas engineer job?
Ideal Heating says fixing a water pipe is usually a job any plumber can do. If the water is coming from the boiler itself, that is a job for a Gas Safe registered engineer.
Sources
We cite the original source for every figure: government, regulators, standards bodies and manufacturers' own documents. Each one shows the date we last checked it.
- Vaillant. Why is my boiler losing pressure?. Checked 11 November 2026. ↩
- Ideal Heating. Why is my boiler losing pressure?. Checked 11 November 2026. ↩
- Ideal Heating. My boiler is leaking: what should I do?. Checked 11 November 2026. ↩
- Glow-worm. Why is my radiator cold at the bottom?. Checked 11 November 2026. ↩