How to Bleed a Radiator and Determine If You Need New Ones

How to bleed a radiator

Primarily, bleeding a radiator involves letting out trapped air inside the central heating system. This is an issue that’s common among un-vented heating systems. When trapped air prevents water from heating the whole radiator, cold spots are created.

Hearing clicking or flowing sounds from the radiator is also a sign it needs bleeding. If you notice that your radiator’s top section is cooler than the bottom half, your heating system is not working efficiently.

Bleeding Radiators: Your Step-By-Step Guide

Bleeding a radiator is an easy and straightforward task. Before bleeding air from your radiator system, ensure you have the following handy:

  • A radiator bleed key (needed to open up the radiator vent valve)
  • A towel or cloth (needed to catch drips)

Step 1: Turning your heating on

Prior to bleeding, you need to turn on the heating first to warm up all the radiators. This is also necessary so pressure that is built-up by the heating will push all the unwanted air out.

Step 2: Identifying the radiators that need bleeding

Check each radiator for cold spots. What are some of the signs you need to look out for? If your radiator takes a long time to heat up, you notice cold spots, or you hear gurgling sounds, it is likely that there’s trapped air in the radiator. The trapped air prevents the water from filling the radiator.

Word of caution: Since the radiators will be very hot, you need to be extra careful. Wearing a pair of thin gloves is recommended so you don’t burn yourself.

turn off your central heating system

Step 3: Turning off your central heating

This is very important: you need to switch off the central heating system before bleeding the radiator. If the heating is on, you’ll risk covering the floor with water and worse, scalding yourself.

Step 4: Preparing the area

When bleeding an old radiator, water can become discoloured. Save yourself all the trouble by placing old towels on the carpet. This is especially necessary if you have light ones.

Step 5: Opening up the radiator bleed valve

Insert the radiator bleed key into the bleed valve. In most cases, the bleed valve is situated at the top of the radiator, to the side. As soon as you insert the radiator key into the valve, you will feel them lock together.

Turn the valve anti-clockwise carefully. As the air starts to escape, you will hear a hissing sound. Keep sufficient distance and be careful as the air could be hot.

Step 6: Bleed the radiator

Avoid opening the valve fully when you bleed air from the radiator as water can come rushing out. A quarter to half a turn would suffice. Continue to hold the radiator bleed key until the air stops coming out. 

When you notice that only water is dripping from the radiator, then the bleeding process is complete. Turn the bleed valve clockwise to seal the radiator and ensure you do not over tighten.

Step 7: Repeat the process on all your radiators

It is crucial that you bleed all the radiators you have in your property. It is recommended that you start from the ground floor and work your way up since the air rises through the system.

Step 8: Check your heating system’s pressure

Once the task of bleeding all your radiators has been completed, you need to re-pressurise your heating system. There is always a tendency to lose some water when you bleed your heating system’s boiler. 

If a large amount of water is lost, your system will have difficulty heating the top floors. It is also possible for the central heating system to fail entirely. If the water pressure is correct, the needle gauge will be facing green. If it’s on yellow, re-pressurising the system is necessary. 

Need Radiator Replacement? Common Signs to Look Out For!

At times, bleeding your radiator won’t suffice and replacing it is the ultimate solution. Here are some red flags to look for that might indicate a radiator replacement is due.

It needs to be bled more than usual

Bleeding the radiator is often the solution when they are not heating up fully or when they seem colder than usual. However, if you notice that most of the radiators in the house need bleeding then it can be a glaring sign of an inherent problem. 

If you’re unsure, consider it best to get in touch with us. We can assess if a flush is all your system needs or there are other issues that need immediate attention.

Do the same with other radiators

You hear noise in the heating system

If you hear constant noises each time you turn your heating on, it is likely that there’s an issue with the internal mechanism of the radiators. 

You notice a spike in the running cost for your central heating system

This is another obvious sign that your boiler or radiator may be malfunctioning. One thing many people miss is the size of the radiator. Small ones need to run hotter to make a room comfortable. Larger ones on the other hand can run at lower temperatures to keep the heat at the right level.


If you notice your heating system is not working accordingly, avoid tinkering things yourself, no matter how tempting. Even if you have good DIY knowledge, you might not have the expertise needed to assess the system as a whole.

If you need your radiators replaced, we can help! We are based in Durham and cover all areas of the Northeast including Bishop Auckland, Newton Aycliffe, Thornaby, Stanley, and many more!