Bleeding radiators is one of those home maintenance tasks that sounds technical but is actually very straightforward. If your radiators have cold spots at the top — or just aren’t heating as well as they should — here’s exactly how to sort it, step by step.
What You’ll Need
- A radiator bleed key (available at any DIY store or plumber’s merchant for £1–£2)
- An old cloth or small bowl to catch drips
- A flat-head screwdriver (some modern bleed valves use a slot instead of a square key)
Step 1: Turn Your Heating On
Switch on your central heating and allow it to fully warm up — usually 10–15 minutes. This lets you identify which radiators have cold spots and confirms where air is trapped.
Step 2: Identify the Problem Radiators
Feel each radiator carefully. If the top section is noticeably cooler than the bottom, air is trapped there and the radiator needs bleeding. Make a mental note of which radiators need attention.
Step 3: Turn Off the Heating and Wait
Turn off your heating and allow the system to cool for around 30–60 minutes. This prevents scalding hot water from spraying when you open the valve. You should still be able to feel warmth in the radiators — just not boiling hot.
Step 4: Find the Bleed Valve
The bleed valve is a small square-headed bolt at the top corner of the radiator — usually on one of the upper ends. This is where you insert the bleed key.
Step 5: Bleed the Radiator
- Place your cloth or bowl under the valve to catch drips
- Insert the bleed key and turn it slowly anti-clockwise — about a quarter to half a turn
- You’ll hear air hissing out as it escapes — this is exactly what you want
- Hold the key in position and wait for the hissing to stop
- When water starts to drip from the valve, air has been fully released — close the valve by turning clockwise
- Don’t over-tighten; just firm enough to stop the drip
Repeat this for every radiator that had cold spots, working from the ground floor upwards.
Step 6: Check Your Boiler Pressure
Bleeding radiators releases water from the system, which can cause the boiler pressure to drop. After bleeding, check the pressure gauge on your boiler. It should read between 1 and 1.5 bar when cold.
If the pressure has dropped below 1 bar, you’ll need to repressurise the system using the filling loop (usually a silver braided hose under the boiler). Your boiler manual will show you how, or call PPS Gas & Electric for guidance.
Step 7: Test the System
Turn your heating back on and allow it to warm up fully. Check the previously cold radiators — they should now be heating evenly from top to bottom.
When DIY Isn’t Enough
If your radiators remain cold after bleeding, or if they need bleeding repeatedly, there may be a deeper issue — a system leak, a failing pump, or significant sludge buildup. In this case, contact a Gas Safe engineer from PPS Gas & Electric who covers Leamington Spa, Warwick, and across Warwickshire.
Call PPS Gas & Electric on 01926 778709 or visit ppsgas.com to book your appointment today.
