How to Bleed a Radiator (Step-by-Step Guide)

If your radiator feels cold at the top but warm at the bottom, there’s a good chance it needs bleeding. This common issue is caused by trapped air in the heating system, which stops hot water from circulating properly.

At Pleasant Plumbers, we help homeowners across London restore their heating system’s efficiency with simple maintenance tips like this one. Here’s your step-by-step guide to bleeding a radiator safely and correctly.

Bleeding your radiators helps:

• Improve heat circulation
• Reduce energy bills
• Eliminate cold spots
• Reduce strain on your boiler

Over time, air builds up in radiators, especially after you’ve had a boiler serviced, a power flush, or during the colder months.

• Radiator bleed key (or a flathead screwdriver for modern valves)
• An old cloth or towel
• A jug or bowl to catch water
• Optional: gloves (radiators may be hot)

Step 1: Turn Off Your Heating

Before bleeding, switch off your central heating and wait until the radiators have cooled. This prevents hot water from spraying out and gives you an accurate pressure reading.

Step 2: Identify the Radiator Valve

Locate the small valve at the top corner of your radiator — usually on the side. Insert the radiator key or screwdriver into the valve.

Step 3: Place Cloth and Bowl Below Valve

Use a towel or bowl underneath to catch any water that escapes during bleeding.

Step 4: Slowly Turn the Key Anti-Clockwise

You’ll hear a hissing sound — that’s air escaping. Once water begins to flow steadily, tighten the valve by turning the key clockwise. Do not over-tighten.

Step 5: Check Boiler Pressure

After bleeding, your boiler pressure may have dropped slightly. Check the boiler pressure gauge and top up if necessary using the filling loop (aim for around 1.5 bar when cold).

Step 6: Repeat for All Radiators

Start with the radiator furthest from your boiler and work your way closer.

If your radiators are still cold after bleeding, there may be:

• Sludge or debris buildup
• Faulty valves
• Imbalance in your system
• Boiler pressure issues

That’s when it’s time to call a trusted heating engineer in London like Pleasant Plumbers. We’ll diagnose the issue and get your heating working efficiently again.

From radiator repairs to full system power flushing, Pleasant Plumbers is trusted across London for reliable, friendly service. Whether you live in a flat, terraced house, or townhouse, we’ll help you stay warm this winter.

📲 Call or WhatsApp 0800 046 1000

📧 Email [email protected]
🌐 Visit pleasantplumbers.com

Pleasant Plumbers – Keeping London homes warm, efficient, and flowing smoothly.