Leaks
Radiator Leaking Water? Do This First
Reviewed by our Gas Safe registered engineers · Last updated 22 July 2026
If a radiator is actively leaking and water is spreading, the priority is to stop the flow and protect your floors — then find the source. Here’s exactly what to do, in order. To diagnose a slow drip by where it’s coming from, see our radiator-leak causes guide.
Quick answer: Put a bowl and towels under the leak, then turn both valves at the ends of the radiator fully clockwise to isolate it — that stops fresh water reaching the leak, so it can only drip out what’s already inside. Mop as you go to protect the floor. If the water is running fast, coming through a ceiling, or near electrics, turn off the water supply and call us now.
How Urgent?
Is it an emergency?
Not every radiator leak is an emergency. The colour on the left shows what you can safely handle yourself and what needs us out quickly.
| The situation | How urgent | What to do |
|---|---|---|
| Slow drip from a valve, water contained | Not an emergency | Isolate the radiator with both valves and put a towel down, then book a repair |
| Steady leak spreading across the floor | Urgent | Isolate the radiator and mop up; if it keeps coming, turn off the water and call us |
| Water dripping through the ceiling below | Emergency | Turn off the water supply, keep clear of light fittings, and call us now |
| Leak only once the heating warms up | Book a repair | Isolate the radiator; an engineer will re-make the joint |
| Damp patch in the middle of the panel | Needs replacing | The radiator has corroded through and needs replacing |
| Valve nut weeping slightly | Minor | Nip up the nut a quarter-turn; if it still weeps, book a repair |
First Steps
What to do right now
Do this now
- Put a bowl and thick towels under the leak to protect the floor
- Turn both valves at the ends of the radiator fully clockwise to isolate it
- Mop and dry as you go so the water can’t spread or soak in
- Note where the water is coming from so we can bring the right parts
Call us straight away if…
- Water is running fast or spreading into other rooms
- It’s dripping through a ceiling or near light fittings and electrics
- You can’t stop the flow by closing the radiator valves
- The leak is from the middle of the radiator panel (corroded through)
Engineer Insight
Why isolating early matters
Nine times out of ten an emergency radiator leak is at a valve, and closing both valves buys you time until we arrive — the radiator can only leak out the water already inside it. The exception is a panel that’s rusted through: you can’t isolate your way out of that, so catch the water and get the supply off. Whatever the cause, isolating early is what saves your flooring and the ceilings below.
Costs
What repairs typically cost
Typical North London guide prices — you’ll always get an upfront quote before any work starts.
FAQs
Radiator leaks — your questions answered
How do I stop a radiator leaking until a plumber arrives?
Close both valves at the ends of the radiator by turning them fully clockwise. That isolates it, so no fresh water reaches the leak and it can only drip out what’s already inside. Catch the water with a bowl and towels.
Is a leaking radiator an emergency?
A slow, contained drip isn’t — isolate it and book a repair. It becomes an emergency when water is spreading fast, coming through a ceiling, or near electrics. Then turn the water supply off and call us straight away.
Can I turn my heating off to stop a radiator leak?
Turning the heating off lowers the pressure a little, but it won’t stop the leak — closing the radiator’s own valves is what isolates it. Do both: valves off, then heating off.
Will one leaking radiator affect my boiler?
Not directly, but a leak lowers system pressure, and if it drops too far the boiler will lock out. Topping up masks it — the leak still needs fixing, or the pressure keeps falling.
There’s now a stain on the ceiling below — what do I do?
Treat it as urgent: turn off the water supply, keep away from light fittings in the room below, and call us. See our ceiling-leak guide for making the area safe.
Related
Related guides
Diagnose a slow drip by exactly where it’s coming from.
Read guideLeaksBoiler Leaking WaterIf the leak is at the boiler, not a radiator.
Read guideLeaksCeiling Leak From Bathroom AboveWhen a leak has already reached the ceiling below.
Read guidePressureBoiler Losing PressureA radiator leak is a common cause of dropping pressure.
Read guideRadiatorsHow to Bleed a RadiatorDon’t mistake a weeping bleed valve for a real leak.
Read guideEmergencyBoiler Breakdown EmergencyWhat to do if the boiler has stopped as well.
Read guideBrowse all Leak guides, or head back to the Help & Advice Centre.
Radiator leaking right now? We’ll come to you.
Book a Gas Safe engineer to isolate and repair the leak, or call — we keep 24/7 emergency slots across North London for leaks that won’t wait.
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