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If your radiator feels cold at the top and heated at the bottom, it is likely that the air is stuck inside. This air prevents hot water from filling the radiator. As a result, the heating system becomes less efficient, and your house is colder than you want.
This problem can be cured by bleeding your radiators. This is a simple task, and you don’t have to be an expert to do so. This guide will drive you through the process from the Radiator in the UK, what devices you need, and what safety tips to follow.
We will also answer some common questions, such as how to bleed the radiator without a key, if you have a combi boiler, or if you have an old radiator, how to do it.
What Is Radiator Bleeding?
To bleed a radiator means letting the fixed air enter. When the air is in the system, it prevents warm water from flowing properly. This makes your radiator less effective.
You might notice:
- The top of the radiator seems cold.
- The radiator makes noise from gargals or bubbling.
- Your house is not as hot.
- Your kettle works harder than as much as you should.
Bleeding the radiator releases this trapped air and allows the water to fill the entire radiator again. This improves heat output and reduces energy waste.
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Tools You’ll Need
Here are the tools you’ll need before you begin:
- Radiator key – Usually a small square tool that opens the bleed valve.
- Cloth or towel – To catch any water that comes out.
- Bowl or container – Useful if there’s a lot of water.
Tip: If you have lost the radiator key, don’t worry! You can still bleed your radiator by using a flat screwdriver in most cases. Learn how to bleed the radiators without a key.
How to Bleed a Radiator UK? Step-by-Step
1. Turn Off the Heating
Do not bleed radiators while the heating is on. This is very important.
Why? If the water is hot, it could burn you. Also, the system pressure will be higher, which may cause water to spray out quickly.
Wait until the radiators are completely cool. This ensures a safe and clean process.
2. Find the Bleed Valve
Look at the top corner of your radiator. You’ll see a small valve, often with a square shape inside. That’s the bleed valve. Some radiators have a slot instead, which you can open with a flathead screwdriver.
3. Insert the Key or Screwdriver
Place your radiator key (or screwdriver) into the bleed valve. Make sure you have your cloth or towel ready to catch any drips. Turn the key or screwdriver slowly anti-clockwise (to the left).
4. Listen for the Hissing Sound
As soon as you turn the valve, you will hear a hat sound. This fixed air is survival. Keep the valve open until the cast stop and a small amount of water begins to get out.
IMPORTANT: As soon as the water comes out, turn off the valve quickly by turning clockwise (at the far right). Don’t tighten it too much.
5. Check Your Boiler Pressure
When all your radiator becomes bleeding, go to the boiler and check the pressure gauge. If the pressure has fallen below 1 time, make it up with the filling loop (if you are unsure, then check the boiler manual).
Proper pressure (usually between 1 to 1.5 times) is important to drive well.
6. Turn the Heating Back On
After everything is done, switch the heating back on. Wait a few minutes and check if the radiator is now warm from top to bottom.
If it is, great job! You’ve successfully bled your radiator.
How to Bleed Radiators Without a Key?
Many people wonder how to bleed radiators without a key. It’s possible using the right kind of screwdriver.
Here’s how:
- Look at the bleed valve. If it has a slotted groove, you can use a flathead screwdriver.
- Insert the screwdriver and turn anti-clockwise slowly.
- Follow the same steps as you would with a radiator key.
- Be ready with a cloth to catch any water.
Note: If the valve is square-shaped without a slot, you’ll need to buy a replacement key. These are available at most UK DIY shops for under £2.
How to Bleed Radiators with a Combi Boiler?
If you have a combi boiler, the process is the same as any other system. But there’s one key difference – bleeding radiators can cause a pressure drop in combi systems, which may trigger an error on your boiler.
Here’s what to do:
- Bleed your radiators one at a time.
- After each one, check the boiler pressure.
- If it drops below 1 bar, repressurise your system using the filling loop.
- Once pressure is back to normal, continue with the next radiator.
This prevents the system from shutting down or locking out.
How to Bleed an Old Radiator?
Old radiators might be rusty or stiff. The valve may also be tight or stuck.
Here’s how to bleed an old radiator:
- Use WD-40 or a similar lubricant if the valve is stiff.
- Be very gentle when turning the valve. Forcing it can break it.
- You may need to wear gloves to get a better grip.
- If the radiator hasn’t been used in years, expect more air or dirty water.
After bleeding, check for leaks or corrosion around the valve. If you notice damage, contact a heating engineer to inspect it.
Safety Tips When Bleeding Radiators
- Always turn the heating off and wait for radiators to cool down.
- Have a towel or cloth ready to avoid mess.
- Don’t open the valve too much – just a small turn is enough.
- Use the right tool – don’t force a screwdriver into a square valve.
- Be cautious with very old systems or ones with visible damage.
- After bleeding, always check the boiler pressure and top up if needed.
Why You Should Bleed Your Radiators Regularly
Bleeding your radiators is part of basic home maintenance in the UK. It helps:
- Improve heat output
- Save on energy bills
- Reduce strain on your boiler
- Extend the life of your heating system
It’s a good idea to bleed your radiators once a year, usually at the start of the heating season (around autumn). You can also do it whenever you notice uneven heating or strange sounds.
Common Mistakes to Avoid
- Bleeding with the heating on – This can burn you and may cause water to spurt out.
- Not checking boiler pressure – Can lead to low pressure errors and system faults.
- Using the wrong tool – Can damage the bleed valve.
What Happens If You Bleed a Radiator With the Heating On?
This is a very common question, and the answer is simple:
Don’t do it.
Bleeding a radiator with the heating on can:
- Cause hot water to spray out and burn you.
- Lead to inaccurate results, as pressure and temperature affect air movement.
- Damage the system if too much pressure is released suddenly.
Always wait until the system is off and cool before bleeding.
Final Thoughts
Bleeding your radiators is simple, safe and necessary for a warm, energy efficient home. You do not need special skills or expensive equipment. Just follow the steps given above, use the right tools and take your time.
Whether you have a Combi boiler, an old radiator, or you work without any key, now you know how to do the work properly. Keep the heating system in top shape and be comfortable all winter.
Frequently Asked Questions
Yes, if your radiator has a slave bleeding valve, a glass screwdriver will work. Turn gently and be prepared with a towel to catch the drip.
Feel the radiator. If the top is cold but the bottom is hot, it likely has trapped air and needs bleeding. Gurgling sounds are also a sign.
No, always stop the heating and allow the radiators to cool before bleeding. This is for your safety and to get accurate results.
You should bleed your radiators once a year, preferably before winter. Also, bleed them if they feel cold at the top or make strange noises.
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