How to Bleed a Radiator (UK DIY Guide)
If your radiator feels cold at the top but warm at the bottom, trapped air is likely preventing it from heating properly. Bleeding a radiator is a simple DIY task that can improve heating efficiency and reduce energy waste.
This step-by-step UK guide explains how to bleed a radiator safely and when further action may be required.
Tools You’ll Need
- Radiator bleed key
- Cloth or towel
- Small container or cup
- Screwdriver (for some modern valves)
Step 1: Turn Off the Heating
Switch off your boiler and allow the heating system to cool completely.
Bleeding a hot radiator can cause burns.
Step 2: Locate the Bleed Valve
The bleed valve is usually at the top corner of the radiator.
Insert the bleed key securely into the square valve.
Step 3: Open the Valve Slowly
Hold a cloth under the valve.
Turn the key anti-clockwise slowly.
You will hear a hissing sound as trapped air escapes.
Step 4: Close the Valve
Once water begins to trickle out steadily, close the valve by turning clockwise.
Do not overtighten.
Step 5: Check Boiler Pressure
After bleeding radiators, check your boiler pressure gauge.
Most combi boilers should read between 1 and 1.5 bar.
If pressure has dropped, follow manufacturer instructions to repressurise.
Step 6: Turn Heating Back On
Switch the heating back on and check the radiator heats evenly from top to bottom.
Common Mistakes to Avoid
- Bleeding while heating is on
- Opening the valve too far
- Forgetting to check boiler pressure
- Overtightening the bleed screw
- Ignoring persistent cold spots
If radiators repeatedly need bleeding, there may be a deeper system issue.
When to Call a Professional
You should seek professional help if:
- Boiler pressure keeps dropping
- Radiators stay cold after bleeding
- There are leaks from the valve
- The system contains sludge
- You hear banging noises from pipes
See our Heating & Boiler Repair Cost Guide for typical UK pricing.