How To Bleed A Radiator


Guscott Heating Services

how to bleed a radiator

How To Bleed A Radiator

We rely heavily on our radiators to heat our home and that means we want them working as efficiently as possible. Like anything we use frequently, over time the performance of your radiators can reduce slightly. This is why your radiators need bleeding, to remove the excess air and allow the hot water to flow through them properly.

We hope our six steps guide can shed some light on the simple bleeding process to help you increase the efficiency of your central heating, cut your energy bills and make your home warm during the winter months.

What does bleeding a radiator mean?

Your radiators are filled with the hot water that transfers from your boiler. This heat is pushed into a room to make it toasty during the winter months. However, sometimes, excess air in the system can leave your boiler with cold spots.

Bleeding a radiator is the process of letting such excess air out using a radiator bleed key so that there are no cold patches.

How do I know if my radiators need bleeding?

Well, there are some tell-tale signs you can look out for. The most common sign is cold spots or even a whole section of the radiator that doesn’t feel hot. Air is lighter than water, and so you may notice that the radiator is hot at the bottom but cold at the top.

You may also notice unusual noises coming from your radiators, including gurgling and rattling, which is a good indicator that there is trapped air in the system.

Fortunately, bleeding your radiators is a doddle. See below for our recommendation.

How to bleed your radiator step by step

To bleed your radiators, you may require the following tools:

  • A radiator bleed key – used to open up the radiator vent valve (available from most hardware stores or even Amazon)
  • An old cloth or towel – to protect your flooring from dirty water that could escape. 
  • A bowl or jug – to catch any water in.

Step 1: Turn your heating on

Before you can begin bleeding your radiators, you need to assess which ones need bleeding. You can bleed all of them, but some may not contain any excess air. Therefore, you should allow the radiators to warm up and check which ones have cold spots.

Turning the heating on can also help to increase the pressure in the system and will allow any air to rise to the top of the radiators, ready for bleeding. 

Step 2: Turn your heating off

It’s imperative that you don’t bleed your radiators while the heating is on. Hot water could escape from the device and burn you. Therefore, once you’ve made a note of the radiators to bleed, turn the central heating off and wait for at least a couple of hours for the water to cool down.

During this time, pop your old cloth/towels down to protect your flooring. 

Step 3: Use your radiator key to open the bleed valve

Place your bowl or jug underneath the bleed valve and slowly open it using your radiator bleed key.

The valve can be located at the top of the radiator and to the side. It looks like a round hole with a square inside. When you insert the radiator key into the bleed valve, you will feel them lock together.

Carefully turn the valve anti-clockwise – as the air begins to escape, you’ll hear a hissing sound.  A quarter to half a turn will be enough. Never open the valve fully, because once all the air has escaped, the water will start to come out.

Top Tip: If you do not have a radiator vent key it is sometimes possible to use a flat-headed screwdriver on modern radiators.

Step 4: – Close the radiator valve

Once the hissing has stopped or some water has begun to come out of the valve, close it by turning the radiator bleed key clockwise. This will seal the radiator.

Step 5: Repeat the process on all radiators

Repeat this bleeding process with all the radiators that showed signs of trapped air. We suggest starting on the ground floor and working your way up the floors at your property because the air rises through the system.

Step 6: Check the pressure of your heating system

Once you have completed the task of bleeding all your radiators, you will need to re-pressurise your heating system. When you bleed a boiler heating system, you always lose some water. If it’s a large amount then your system may have difficulty heating the top floors of your property or the central heating system can fail to start up due to low pressure.

If the water pressure in your system is correct, the needle gauge on your boiler will be facing green. If it’s on yellow, then you will need to re-pressurise the system. 

To do this you’ll need to locate the central filling loop connected to your boiler. It looks like a tap and is connected to your main water supply; for reference, the pressure in a typical family home is usually between 1.0 and 1.5 bar.

Always turn the tap and slowly adjust the pressure. In the unlikely event that you add too much pressure and the needle faces the red, there is also a bleed tap.

If you’re unsure during this step. Give our team a call and we’d be happy to help guide you through the process.

Our Six-step Summary

  1. Turn your heating on
  2. Turn your heating off
  3. Open the radiator bleed valve
  4. Close the radiator bleed valve
  5. Repeat with all required radiators
  6. Check the pressure of your heating system

When is the best time to bleed radiators?

We typically advise you to bleed your radiators at the beginning of the heating season, before you really need it, but you’ll get just as effective a result whatever the time of year.

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