Radiator cold at the top? What it means and how to fix it
Now the heating’s back on for winter, you might notice one of your radiators isn’t quite pulling its weight. It’s warm at the bottom but cold at the top. It’s one of the most common heating questions we’re asked, and the good news is it’s usually an easy fix you can do yourself in a few minutes.
What a cold top means
A radiator that’s cold at the top and warm at the bottom almost always has trapped air inside. Air rises, so it collects at the top of the radiator and stops hot water from filling it. The result is a room that takes longer to warm up and a boiler that’s working harder than it needs to.
Air gets into heating systems naturally over time, especially after the heating has been off all summer. Bleeding your radiators lets it out.
What you’ll need
- A radiator key (from any DIY shop, and some newer radiators just need a flat-head screwdriver)
- An old towel or cloth
- A small container to catch drips
How to bleed a radiator
- Turn your heating off and let the radiators cool down. Hot water can spray out, so this step matters.
- Find the bleed valve. It’s a small square fitting at one of the top corners of the radiator.
- Hold your cloth underneath, fit the key and turn it slowly anticlockwise, about a quarter to half a turn.
- You’ll hear a hiss as the air escapes. Wait until it stops and a little water starts to come out.
- Close the valve by turning the key clockwise. Don’t over-tighten it.
- Repeat on any other radiators that are cold at the top.
Check your boiler pressure afterwards
Letting air out of the system can make your boiler pressure drop. Take a look at the gauge on the front of your boiler. When the heating is off, it should usually sit around 1 to 1.5 bar (your boiler manual will give the exact figure). If it’s low, you can usually top it up using the filling loop underneath the boiler. If you’re not sure how, just give us a call.
What if it’s cold at the bottom instead?
A radiator that’s warm at the top but cold at the bottom is a different story. That usually points to a build-up of sludge (dirt and rust from inside the system) sitting in the bottom of the radiator. Bleeding won’t fix this one.
Sludge can also make your whole system less efficient and put extra strain on your boiler. A system flush or a magnetic filter can help, and our engineers can take a look and recommend the right fix.
When to call us
- A radiator stays cold after bleeding
- You need to bleed the same radiators again and again
- Your boiler pressure keeps dropping
- Radiators are cold at the bottom or have cold patches in the middle
Any of these can point to something worth a closer look, like a small leak, a sticking valve or sludge in the system. Our boiler repair team can find the cause and get your heating working as it should.
Keep your heating running smoothly
An annual boiler service is the best way to keep your system healthy through the colder months. And with a Custom Heat & Cool Care Plan, repairs are covered up to £500, from just £12.50 a month.
Radiators still not warming up? Book online or call us on 0330 383 0000.
