If your home is feeling a little chilly despite your heating being on, or some radiators are only warming halfway, it might be time to bleed your radiators. For homes with a combi boiler, this is a common maintenance task that’s easy to do but doing it correctly can save you money, keep your heating efficient, and prevent damage to your system. In this guide, we’ll explain why radiator bleeding is necessary, what causes the issue, and step-by-step instructions on how to bleed radiators with a combi boiler.
Why Radiators Need Bleeding
Over time, air can become trapped inside your radiators. This is normal and happens due to:
Water evaporating from the system
Small leaks or refills
New radiators being installed
When air collects at the top of a radiator, it prevents hot water from circulating fully. This can lead to:
Cold spots on the radiator
Increased energy bills
Noisy radiators (bubbling or gurgling sounds)
Pressure drops in your combi boiler system
Essentially, trapped air reduces heating efficiency. Bleeding your radiators ensures that hot water can flow freely, keeping your home warm and your boiler running smoothly.
What You’ll Need
Most combi boilers operate at higher pressure, so it’s important to be prepared to catch water when releasing air.
Before you start, gather the following:
- A radiator key
- A cloth or small towel
- A bowl or container
- Gloves
Step-by-Step Guide:
How to Bleed Radiators with a Combi Boiler
Turn off your heating system
Start by switching off your combi boiler and letting the radiators cool. Bleeding a hot radiator can be dangerous as hot water may escape.Check the boiler pressure
Combi boilers rely on system pressure to circulate water. Check your boiler’s pressure gauge—it should typically be around 1–1.5 bar when cold. Low pressure may require topping up before bleeding.Locate the bleed valve
Look for the small valve at the top corner of your radiator. It usually has a square or slotted end.Prepare your cloth and container
Place your cloth under the valve and hold the bowl underneath to catch any water that might come out.Open the valve slowly
Insert your radiator key and turn it anti-clockwise slowly. You’ll hear a hissing sound that’s the trapped air escaping.Close the valve
When water starts to flow steadily, close the valve by turning the key clockwise. Be careful not to overtighten.Check the pressure again
Bleeding can lower your system pressure slightly. If needed, top up your combi boiler to the correct level.Turn the heating back on
Switch your boiler back on and check that your radiators are heating evenly. Repeat the process if any remain cold at the top.
Common Mistakes to Avoid
Bleeding while the system is hot: Can cause burns and scalding.
Ignoring low boiler pressure: Reduces efficiency and can damage the system.
Overtightening the bleed valve: May damage the radiator or valve.
Skipping regular checks: Radiators benefit from being bled once or twice a year, especially before winter.
When to Call a Gas Engineer
While bleeding radiators is straightforward, some issues require professional attention, such as:
Persistent cold spots despite bleeding
Frequent pressure drops in your combi boiler
Strange noises like banging or gurgling
Leaks from valves or pipes
A qualified gas engineer can check your system, safely restore pressure, and ensure your combi boiler and radiators are working efficiently.
Knowing how to bleed radiators with a combi boiler is a simple trick that keeps your home warmer, reduces energy bills, and prolongs the life of your heating system. Regular maintenance is key, but for any complex issues or if you’d rather not tackle it yourself a professional engineer is the safest and most effective solution.
At Plumbing Immediately, we provide expert boiler and radiator services across London. From routine maintenance to emergency repairs, our certified gas engineers ensure your heating stays reliable all year round. Don’t wait for a cold spot to become a bigger problem book a service today and enjoy a warm, worry-free home.
Book Your Radiator & Boiler Service Today
Don’t let cold spots or inefficient heating ruin your comfort. Our certified gas engineers can inspect, bleed, and service your radiators and combi boiler, ensuring your system runs safely and efficiently all year round. Schedule your service now for a warm, worry-free home.