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How To Bleed A Radiator

Follow these simple steps... 

  1. Turn on your boiler 
  2. Identify which radiators are cold
  3. Place a towel/container below the valve
  4. Bleed downstairs radiators first
  5. Twist your trapped air to escape
  6. Allow trapped air to escape 
  7. Check your boiler pressure is 1.0 - 1.5 bars
  8. Boot up your central heating
  9. Conduct a 'heat test' 

Are your radiators not getting as hot as usual? Are they only warming up towards the bottom or in certain areas? Or are they making some odd noises as they heat up?

It may be time to give your radiators a bleed.

Despite this task sounding slightly menacing, all it involves is allowing any pockets of trapped air to escape. If trapped air is left inside your radiators with nowhere to go, it will cause blockages. This prevents hot water from spreading across your whole radiator.

Having to bleed your radiators doesn’t automatically mean that there is a larger or more serious issue with your central heating, so don’t get on the phone to your engineer straight away. It’s simply something that needs doing regularly to allow your heating system to do its job - to keep you cosy.

Bleeding your radiators on a semi-regular basis (around every two months) means your central heating can run efficiently and you can rest easy knowing that you’re keeping a lid on your energy bills.

So, let’s take a closer look at how to bleed a radiator. It’s easy and quick - so there really is no excuse for neglecting your radiators!

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How to identify if you need to do some radiator bleeding

Luckily, it’s easy enough to spot whether your radiators will need bleeding:

  • Is your radiator cold at the top? If so, this probably means it’s time to bleed it. The bubbles from trapped air rise and gather mostly towards the top end of your radiator, which causes it to be colder than the bottom half.
  • Are there any damp patches or condensation surrounding your radiator or above it?
  • Does your radiator make some funny noises when heating up? These creaky sounds are caused by the irregular air pressure causing vibrations.

What will you need for radiator bleeding?

  • A radiator key
  • A cloth or glove
  • Old towel(s)
  • Container

So not a lot really! You probably have everything you need around your home already. The only item you may be missing is a radiator/bleeding key, which you can find in most DIY shops, large supermarkets, or online - for a small price.

Next, let’s get to business and learn how to bleed radiators.

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Simple steps for bleeding a radiator 

 1. Have a feel around!

Bleeding radiators is a relatively simple job. Start off by turning your boiler on and allowing your radiators plenty of time to fully heat up. This way, you can easily identify which radiators need some TLC and which can be left alone.

Have a feel around the surface of your radiators (without burning yourself!) for any cold patches. If any make a funny noise when heating up, have patches that heat doesn’t reach or you notice a radiator is cold at the top, it is definitely worth bleeding them to stop your energy bills from shooting up. Everyone's worst fear!

Why not just bleed all your radiators to be on the safe side, you might ask? This can actually do more harm than good. If you bleed a radiator with no trapped air inside you risk your boiler pressure dropping too low and your whole heating system failing - not what you want.

You might be thinking, ‘do you bleed a radiator with the heating on or off’ - the answer is off, definitely off. If you attempt to bleed a radiator with your heating on, you risk hurting yourself with the hot air or water from your radiators. You don’t want any trips to A&E just from trying to bleed a radiator.

So, once you’ve pinpointed which radiators to bleed, turn your heating off. It’s no good being impatient and attempting to bleed radiators when hot or cold - be on the safe side and allow your radiators plenty of time to cool down.

2. Set the trapped air free! 

Next, you can get stuck into your radiator bleeding and remove the air blockages from your boiler. We would recommend starting at the bottom and working your way up. In other words, bleed your downstairs radiators first, then move onto upstairs.

Before you get stuck into opening your radiator valves, make sure your lovely home is protected from any dirty radiator water spillages. Place an old towel and a container below the valve to catch any liquids.

Now that your carpet or flooring is protected, make sure you are too. Use an old cloth or thick glove to twist your radiator key anti-clockwise and open the valve.

Keep in mind that you shouldn’t get carried away and open your radiator valve completely or keep it open for too long - too much water will pour out and your boiler pressure will drop dramatically. Simply turn the valve enough to hear the hissing noise of air escaping. Allow all the trapped air to escape until the sound stops and a steady stream of water starts to leak from the valve. This means that you have mastered how to bleed radiators and can re-tighten your valve - well done!

To avoid any rust forming around your radiator valve, be sure to wipe away any excess moisture or condensation once you’ve finished.

 3. Check it’s worked. 

The third and final step in how to bleed a radiator involves double-checking that your efforts have paid off.

Firstly, check your boiler pressure. It’s normal for your pressure to decrease slightly after radiator bleeding. However, for reference, it should be around 1.0 - 1.5 bars when switched off or around 2 bars when switched on.

Has your pressure gauge dropped too low? If so, you may have to repressurise your boiler using a filling loop or call out your engineer to give you a helping hand.

If your boiler pressure appears fine, it’s time for a ‘heat test’. Boot up your central heating and have another feel of your radiators. All being well, there should be no more cold patches, meaning you and your family can feel the full benefits of a warm home and save some cash on your bills - it’s a win-win situation.

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Has bleeding radiators made no improvements?

Radiator bleeding is a job that should only need doing every two months. If you find that you seem to have consistent and frequent issues with cold spots on your radiators, despite bleeding them regularly, there is probably a more serious issue that needs attention.

In this case, check around your home, boiler, and underneath radiators for any leaks that could be causing trouble. Leaks can present themselves as damp patches or puddles, or could also be identifiable by rust.

If you can’t find any leaks and find a radiator cold at bottom, you may need your system flushing to reduce the build up of sludge. Over time, dirt naturally collects inside your boiler, within your pipes and at the bottom of your radiators - draining this dirty water away can allow the hot water to flow around your home with no restrictions.

If you are a boiler novice, which most of us tend to be, it is worth involving an engineer to help drain and power flush your system. They will carry out the process in a safe manner, without damaging your home, and help to identify any potential leaks and faults around or within your boiler too.

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Why should you bleed radiators regularly? 

As well as the results of bleeding a radiator having immediate benefits like a cosier, more efficient, and environmentally-friendly home - there are long term positive effects too.

If you fail to consider radiator bleeding at all, you risk damaging your boiler in the long run and drastically limiting its lifespan. Having to replace a boiler is something we all dread, so the more you can do to prevent this, the better! You might think you are too busy to spend time bleeding radiators, but a small amount of effort can really make a difference in the long run.

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Followed all these radiator bleeding steps and still having trouble?

If you find that some of your radiators still feel cold in places even after bleeding them, it is worth giving an engineer a call - you don’t want your money to go down the drain!

Most of the time, an engineer can identify and fix any heating issues fairly easily. Unfortunately though, sometimes it’s best to accept defeat and replace your old boiler and/or radiators.

BOXT provides a simple boiler matching service, so you can find a replacement boiler that suits you and your home down to the ground. Answer some quick questions and discover your options today!

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