Radiators
Radiator Cold at the Top? How to Fix It
Reviewed by our Gas Safe registered engineers · Last updated 22 July 2026
A radiator that’s cold at the top but warm at the bottom almost always means trapped air — and bleeding it is a quick, safe fix. Here’s how to sort it, and when it points to something more.
Quick answer: Cold at the top, warm at the bottom is trapped air. Bleed the radiator with a radiator key (heating off, radiators cool) until air stops hissing and water trickles out, then top the boiler pressure back up to ~1.3 bar. If it keeps happening, air is getting in and it’s worth a check.
Common Causes
Why a radiator is cold at the top
The colour on the left shows whether it’s a safe homeowner check or a job for an engineer.
| What you feel | Likely cause | What to do |
|---|---|---|
| Cold at the top, warm at the bottom | Trapped air | Bleed the radiator |
| Still cold at the top after bleeding | More air, or a system issue | Bleed again and check the boiler pressure |
| Several radiators cold at the top | Air across the whole system | Bleed them all; check the feed and pump |
| Cold at the top with gurgling | An air pocket | Bleed the radiator to release it |
| Needs bleeding again and again | Air getting in (leak or corrosion) | An engineer should check for a leak or failing part |
| Cold at top and pressure won’t hold | A leak drawing in air | Book an engineer to trace the leak |
Safe Checks
What you can safely do
Safe to do
- Bleed the radiator with a radiator key (heating off, rads cool)
- Top the boiler pressure back up to ~1.3 bar afterwards
- Bleed the furthest radiators first, working back to the boiler
- Check the pressure holds over a few days
Book an engineer if…
- The same radiator needs bleeding repeatedly
- The boiler pressure keeps dropping
- You can see or smell a leak near a radiator or valve
Engineer Insight
What we usually find
Cold-at-the-top is the most DIY-friendly radiator fault there is — a two-minute bleed. The only time it means more is when the same radiator keeps filling with air: that usually points to a small leak or corrosion drawing air in, and topping up pressure repeatedly just masks it. We’ll trace the source so it stays fixed.
Costs
If you’d rather we did it
Typical North London guide prices — you’ll always get an upfront quote before any work starts.
FAQs
Cold at the top — your questions answered
Why is my radiator cold at the top?
Air has risen to the top of the radiator and is stopping hot water filling it. Bleeding the radiator releases the air and lets it heat evenly again.
How do I fix a radiator cold at the top?
Bleed it — heating off and radiators cool, hold a cloth under the bleed valve, open it a quarter-turn until water trickles out, close it, then top up the boiler pressure. Our step-by-step guide has the detail.
Why does the same radiator keep going cold at the top?
If it fills with air again and again, air is being drawn in — usually a small leak or internal corrosion. That’s worth an engineer’s check rather than repeated bleeding.
Is a radiator cold at the top dangerous?
No — it’s a common, harmless efficiency issue. It just means the room won’t warm as well until you release the air.
Do all my radiators need bleeding if one is cold?
Not necessarily, but if several are cold at the top it’s worth bleeding the lot — start with the ones furthest from the boiler and work back.
Related
Keep troubleshooting
The step-by-step fix for cold-at-the-top radiators.
Read guideRadiatorsRadiator Cold at the BottomThe sludge problem — and why bleeding won’t help.
Read guideRadiatorsRadiator Not Getting HotStuck TRVs, closed valves and balancing.
Read guidePressureHow to Repressurise a BoilerTopping the pressure back up after bleeding.
Read guidePressureBoiler Losing PressureIf bleeding keeps dropping the pressure, look here.
Read guideHeatingRadiators Cold But Boiler WorkingWhen several radiators stay cold at once.
Read guideBrowse all Radiator guides, or head back to the Help & Advice Centre.
Radiator won’t warm up? We’ll sort it.
If bleeding doesn’t hold, book a Gas Safe engineer to check for a leak or balance the system — or call for a quick steer first.
Gas Safe Registered 918817 | North London specialists | Upfront pricing