How to Bleed a Radiator

A Step-by-Step Guide from Went’s Heating Services Ltd

Over time, air can build up inside your radiators, reducing the efficiency of your heating system and leaving cold spots at the top of your radiators.

Bleeding your radiators is a simple yet essential maintenance task that helps restore heat flow and keeps your home warm and energy-efficient.

At Went’s Heating Services Ltd, we’re here to walk you through the process — and help you spot when it’s time to call in the professionals.

🛠️ Why Bleeding Radiators Is Important

When air becomes trapped inside your radiators, it prevents hot water from circulating properly. This can cause:

Cold spots at the top of the radiator
Gurgling or banging noises
Slower heating
Increased energy bills due to inefficiency

Bleeding the radiator releases the trapped air, allowing hot water to fill the entire unit and distribute heat evenly.

🧭 When Should You Bleed Your Radiators?

You should consider bleeding your radiators if you notice:

🔸 Cold at the top, warm at the bottom
🔸 Some radiators not heating at all
🔸 Gurgling or knocking noises
🔸 A noticeable rise in your energy bills

🕒 Best Time to Bleed Radiators

Always bleed your radiators when the heating system is off and completely cool. Bleeding them while the system is hot can be dangerous — hot water or steam could escape, risking burns.

⚠️ Can You Bleed a Radiator While the Heating Is On?

Technically yes, but we strongly advise against it. When the heating is on:

The system is pressurised
Hot water or steam could be released
It’s more difficult to monitor pressure changes accurately

Always wait for the system to cool before bleeding.

✅ How to Bleed a Radiator – Step-by-Step

What you’ll need:

Radiator key (or flathead screwdriver)
Cloth or container to catch any water

Step 1: Turn off your heating and let the system cool completely
Step 2: Locate the bleed valve at the top side of the radiator
Step 3: Insert the radiator key and turn anti-clockwise slowly
Step 4: Listen for a hissing sound (that’s the air escaping)
Step 5: When water starts to trickle out, turn the valve clockwise to close it
Step 6: Check the boiler pressure and top it up if it’s dropped below 1 bar

🔧 How to Bleed a Radiator Without a Key

For some radiator types, you can use a flathead screwdriver. The process is the same — just be gentle and always have a cloth ready to catch water.

⏱️ How Long Should It Take?

Most radiators only take 1–2 minutes to bleed. If the air keeps coming or no water appears, there may be a larger issue — such as a blockage or system fault — that needs professional inspection.

📉 Boiler Pressure Too High? Here’s What to Do

If your boiler pressure is too high (above 2.5 bar), try these steps:

Turn the heating off
Wait for the system to cool
Use the pressure relief valve (if fitted) or consult your manual
Do not bleed multiple radiators just to lower pressure — this can lead to air re-entering the system

If you're unsure, call a professional.

🧊 Radiator Still Cold After Bleeding?

If your radiator still isn’t heating properly after bleeding, the issue could be:

Low system pressure
A blocked radiator
A faulty thermostatic valve
Air still trapped in other parts of the system

Let our engineers take a look — we offer full system diagnostics and radiator flushing services.

🛠️ How Often Should You Bleed Radiators?

You don’t need to bleed radiators frequently. We recommend:

Once or twice a year
Before turning the heating on for winter
Anytime you notice cold spots or noise

💬 Need Help? Contact the Heating Experts

If you’re unsure about any part of the process — or your heating system still isn’t performing as it should — we’re here to help.

At Went’s Heating Services Ltd, we provide:

Full heating system checks
Power flushing and diagnostics
Emergency callouts

📞 Call us on: 07554 448 238
📧 Email: info@ilwent.co.uk
📍 Serving: Shropshire, Powys, and Herefordshire