Bleeding a radiator is an essential part of home heating maintenance. Over time, air can become trapped inside your central heating system, causing some radiators to feel cold at the top or heat unevenly. In this guide, we explain how to bleed a radiator safely and effectively, what tools you need and when to call a professional.
What does bleeding a radiator mean?
Bleeding a radiator means releasing trapped air from the central heating system. When air builds up, it prevents hot water from circulating properly, leading to cold spots and reduced efficiency. By bleeding your radiators, you allow the water to flow freely again, improving heat output and saving on energy costs.
According to the Energy Saving Trust, regular maintenance of your heating system, including radiator bleeding, can help improve overall efficiency, save carbon and reduce energy bills.
How to tell if your radiator needs bleeding
You can usually tell when a radiator needs bleeding by checking for the following signs:
- The top of the radiator feels cooler than the bottom
- You hear gurgling or bubbling noises from the radiator
- The entire radiator stays cold even when the heating is on
- It takes longer than usual for rooms to warm up
If you notice these symptoms, it is likely that air has become trapped inside and the radiator needs to be bled.
What you need before bleeding a radiator
Before starting, make sure you have the right tools and materials. You will need:
- A radiator key (available from most DIY shops)
- A cloth or small towel to catch any drips
- A bowl or container to catch water
- Protective gloves (optional)
Ensure your central heating is turned off and that the radiators are cool before you begin. Bleeding a hot radiator can cause scalding water to escape.
Step-by-step guide to bleeding a radiator
- Turn off the heating and allow the system to cool completely.
- Locate the radiator bleed valve, usually found at the top corner of the radiator.
- Place the radiator key onto the valve and position a towel or container underneath.
- Turn the key slowly anti-clockwise. You should hear a hissing sound as air escapes.
- Once water starts to come out steadily, tighten the valve again by turning it clockwise.
- Check the radiator for leaks and wipe away any excess water.
- Repeat the process for other radiators in your home if necessary.
After bleeding, check the pressure on your boiler. If it has dropped below 1 bar, you may need to top it up using the filling loop. The Which? guide on topping up boiler pressure explains how to do this safely.
How often should you bleed your radiators?
It is a good idea to bleed your radiators at least once a year, preferably before winter begins. You should also bleed them any time you notice uneven heating or cold spots. Regular maintenance helps your heating system work more efficiently and can extend its lifespan.
Common problems after bleeding a radiator
In some cases, you may notice problems after bleeding your radiators. These can include:
- Low boiler pressure – Check the pressure gauge and top up if needed.
- No heat from one radiator – The valve may be stuck or the radiator might need balancing.
- Persistent gurgling sounds – There could still be air in the system, or you may need professional help.
If problems persist, it is worth contacting a qualified engineer. The Gas Safe Register lists certified heating professionals in your area who can carry out safe repairs and servicing.
Preventing air build-up in radiators
Air can enter your central heating system due to small leaks, corrosion or pressure fluctuations. To prevent air build-up, you can:
- Have your heating system serviced annually
- Install an automatic air vent if air problems are frequent
- Check the boiler pressure regularly
- Ensure all valves are fully open when heating is running
Keeping your system well maintained will help reduce trapped air and ensure your radiators heat evenly throughout your home.
When to call a professional
If you are unsure about bleeding your radiators or encounter persistent heating issues, it is best to contact a professional heating engineer. A trained specialist can identify underlying issues such as sludge build-up, leaks or pump problems that may not be visible.
For reliable advice and local engineers, visit the Chartered Institute of Plumbing and Heating Engineering (CIPHE).
What to remember:
- Bleeding radiators removes trapped air and improves heating efficiency
- You only need a radiator key, a towel, and container to catch water
- Always switch off your central heating and allow it to cool before you start, and check your boiler pressure afterwards
- If problems continue, contact a Gas Safe registered engineer for help
