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Why is my radiator cold?

Feeling the chill with cold radiators even though the heating is on? Here’s how to fix it.

If your central heating is switched on but you’re not feeling the full benefit because your radiator feels cold to the touch, then not only are you wasting money on ineffective heating, but you’re cold too!

The good news is, there’s often a very simple fix, which you can do yourself. Read on and you’ll soon be feeling warm and toasty all over.

Why is my radiator cold at the top?

bleeding a cold radiator

If your radiator is hot at the bottom, but cold at the top, it’s likely you have air trapped in the top of the radiator.

Fortunately, this is a relatively simple fix that you can do usually do yourself.

To remove the air trapped at the top of a radiator, and allow the heat to disperse evenly, you’ll need to bleed the radiator.

How to bleed a radiator

  • First, turn off the central heating system.
  • Next, locate the bleed valve on the top or side of the radiator.
  • Use a radiator key or a flat head screwdriver to loosen the bleed valve.
  • Air will begin to escape from the bleed valve and you’ll hear a hissing sound.
  • When the hissing sound stops, you’ll get a little water trickling out. This is when it’s time to tighten the bleed valve back up.
  • Turn the central heating system back on.
  • Your radiator should now heat evenly.
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Why is my radiator cold at the bottom?

If your radiator is not heating fully, i.e. your radiator is hot at the top and cold at the bottom, it could be due to sludge, debris, rust, dirt, and even limescale.

Debris accumulating in the bottom of the radiator over time, restricts the flow of hot water to the whole radiator, meaning the bottom of the radiator is not getting hot.

The debris is normally small bits of rusted metal that have flaked off from the inside of the system. The metal and water mix, corrode and settle in the bottom of the radiator. Limescale can also contribute to this, especially if you live in a hard water area.

How to remove sludge from a radiator

The best way to clear out the sludge in a radiator is with a power flush.

If you have the skills, you can remove the radiator from the pipework, take it outside and flush it through with a garden hose.

However, most people opt to call in a qualified plumber for this job. You can expect to pay around £50 per hour for a plumber.

How to fix a radiator that’s not heating

plumber fixing a cold radiatorTo fix a radiator that’s not heating, you may need to bleed the radiator or power flush the radiator.

  • A radiator that’s hot at the bottom, but cold at the top, could have air trapped inside. Scroll up to learn how to bleed a radiator.
  • A radiator that’s cold at the bottom, but hot at the top, may have debris and sludge at the bottom. It’s advisable to call in a professional to do this messy job for you.

There could be other reasons why your radiator is cold, which a plumber can diagnose and fix for you. These include:

  • A stuck valve
  • A balancing issue
  • A problem with the boiler or heat pump
  • A problem with water pressure.
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What does it mean if my radiator is cold?

If the radiator is cold it is likely there is either air trapped at the top, or debris sitting at the bottom.

What to do if a radiator is cold

To fix a cold radiator you will either need to bleed it or power flush it, depending on the cause of the problem. Bleeding the radiator will get rid of trapped air (indicated by the rad feeling cold at the top). A power flush is needed to remove debris (indicated by the rad feeling cold at the bottom). To do this, you’ll need to remove the radiator, take it outside and flush it through with a hose.

What happens if you bleed a radiator with the heating on?

If you bleed a radiator with the heating on, you risk boiling hot water spilling out of the radiator and onto you. It’s recommended to turn your central heating system off before bleeding a radiator.

Should a radiator be hot all over?

Heat rises, so it’s natural for the radiator to feel a little warmer at the top than at the bottom. However, with your central heating system switched on, no part of the radiator should feel completely cold.

Key takeaways

  • If you have a problem with one radiator not heating properly, it could be due to trapped air or a build-up of sludge.
  • Trapped air is normally indicated by a radiator that’s hot at the bottom and cold at the top.
  • Conversely, if the radiator is not heating evenly due to debris, it’ll likely feel hot at the top and cold at the bottom.
  • You can relieve trapped air by bleeding the radiator. Power flushing the radiator will clear any debris inside.
  • There can sometimes be other reasons why your radiator is cold, including a stuck valve.
  • If multiple radiators are cold, this could be due to balancing, the boiler or heat pump, or water pressure.

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