How to Bleed a Radiator

Why do radiators need bleeding?

Before we get into it, let’s just cover the basics.

Over time and through daily use, air gets trapped inside your radiators, stopping hot water from circulating properly and leaving you with cold spots even when the heating's cranked up to full. This can put unnecessary pressure on your boiler as it has to work harder and for longer to heat your home.

Bleeding your radiators releases this trapped air so that hot water can flow freely, and your radiators can heat up fully and efficiently. It’s a simple energy-saving fix that can enhance the performance of your heating system, ensuring your home warms up evenly while keeping your energy consumption — and bills — lower.

You might’ve also heard about draining or flushing your radiator system, but it’s important to note that this is an entirely different process. Flushing or draining your radiators is when you clean out the sediment and sludge that’s accumulated inside your heating system. It’s often the next step if bleeding doesn’t fix your problem, and it requires professional help.

Thankfully, bleeding your radiators is easy to do at home and can be done in a few minutes.

How to bleed a radiator

Ok, this is the really important bit. You’ll be pleased to know that bleeding a radiator is a relatively simple task that you can do on your own with just a few simple tools. Here's how you can get your radiators running hot, evenly, and efficiently:

What you’ll need:

• A radiator bleed key

• A cloth or small towel to catch any drips

• A bowl, jug, or similar container to hold under the valve

If you don’t have a radiator key, you can often just use a flat-blade screwdriver instead. However, this does depend on your radiator valve, so if you're unsure, we’d suggest speaking to a plumber for professional help.

A step-by-step guide to bleeding a radiator:

1. Make sure your heating is turned off
   Start by switching off your heating system and allowing it to cool fully to prevent hot water from passing through the pipes while you work. This makes the process safer and prevents potential burns.

2. Find the radiator valve
   Look for the radiator valve, which is usually in the top corner of the radiator. It's often a small round peg that you turn to release the trapped air.

3. Position your container and cloth
   Place your bowl or jug under the valve to catch any water that might drip out. You’ll also want to hold your cloth in one hand directly below the valve to catch any drips or spray.

4. Open the valve
   With your other hand, insert your radiator key into the valve and slowly turn it anti-clockwise to open it, making sure to open it only very slightly. You should hear a hissing sound as the air escapes. Once the hissing sound stops and water starts to dribble out, it means that all the air has been released.

5. Tighten the valve
   Once the water starts flowing out steadily, close the valve and tighten it by turning the key clockwise.

6. Clean up
   After the valve has been tightened, mop up any water that may have leaked.

7. Relax in your warm and cosy home

Top tip: if you suspect that several radiators in your home need bleeding, start by bleeding the one furthest away from your boiler, as it’s likely to have the most trapped air and repeat the above steps with the rest of your radiators.

What do you need to do after bleeding your radiator?

After you’ve bled your radiators, there are two important steps to make sure everything has gone smoothly: checking your boiler pressure and testing your central heating system.

Check your boiler pressure

Most boilers operate best when they’re within a specific pressure range, which is usually marked on the pressure gauge. If the pressure has dropped too low when you’ve bled your radiators, your boiler may not function properly or could shut down altogether to prevent damage.

To check your boiler pressure, there should be a pressure gauge on the front of your boiler with a dial that tells you whether it’s running at low, normal, or high pressure. A healthy pressure level tends to be between 1.0 and 1.5 when your heating system is turned off and around 2 bars when it’s in use. 

If your boiler is lower or higher than this and hasn’t stabilised after bleeding your radiators, you may need to get your heating system repressurised by a professional.

Test your heating system

If the pressure has adjusted and stabilised, turn on your heating system to check that all radiators are heating up evenly and that there are no signs of leaks or unusual noises.

How often do I need to bleed a radiator

Bleeding your radiators at least once a year should reduce the buildup of significant amounts of air and help your central heating run efficiently.

Annual maintenance should help you release any built-up air before it accumulates and significantly impacts your boiler and energy usage, but the age and condition of your central heating system could also affect it. Older central heating systems or houses in hard water areas are more susceptible to frequent bleeding as there’s an increased risk of mineral deposits building up in the pipes.

If you notice cold spots reforming quickly after bleeding your radiators, you may need to contact your plumber to have your boiler inspected.

When is the best time to bleed a radiator

The best time to bleed your radiators is just before the heating season starts, usually at the beginning of autumn. 

This is because it’s a good idea to check on your heating system when it’s not been used in a while, like during the spring and summer months. Plus, it’s worth checking that everything is running properly and efficiently before you need the heating to warm up your home when temperatures drop in the cooler months.

Read more energy efficiency tips for your boiler.

Why is my radiator still not heating properly?

If you've bled your radiators, but one or more still aren't heating up as they should, there may be other problems with your system. These could be:

• A buildup of sludge at the bottom of your radiator that’s affecting circulation

• Low or high boiler pressure

• An imbalance in your system causes radiators closest to the boiler to be hot but those further away to be cold

• An older central heating system that’s no longer running efficiently

If you aren’t sure what the issue could be, it may be time to call a professional. Persistent heating problems could be a sign that your boiler has a more complex problem, and it’s best to get it checked before it gets worse. In extreme cases, you may need a new boiler installed.

Heat your home with UW

By learning how to bleed a radiator properly, you'll ensure your home heats more efficiently and reduce energy wastage, which can lead to lower heating bills.

Find out how we can help keep your home cosy and warm with Boiler Installation.