What you'll need

Radiator bleed key (or flathead screwdriver)

Small cloth or bowl

Towel

⚠ Safety first

If you're unsure about repressuriing your boiler or if pressure keeps dropping, call a Gas Safe registered plumber. Don't attempt to work on the boiler itself.

Step-by-step guide

Turn the heating on
Run the heating until all radiators are fully warm — usually 10-15 minutes. This builds pressure in the system and makes trapped air easier to identify.
Find the cold radiators
Go around every radiator and feel the top and bottom. A radiator that's hot at the bottom but cold or cool at the top has trapped air and needs bleeding.
Turn the heating off and wait
Switch off the boiler and let the system cool for 30-60 minutes. Working on a pressurised hot system is dangerous — the water that comes out when you bleed can scald.
Locate the bleed valve
The bleed valve is the small square or slotted nut at the top corner of the radiator. Insert your bleed key (or flathead screwdriver) into it.
Open the valve slowly
Turn the key anticlockwise by a quarter to half turn only. You'll hear a hissing sound — that's the trapped air escaping. Hold your cloth underneath to catch any water drips.
Wait for water to appear
Keep the valve open until the hissing stops and a steady stream of water comes out. This means all the air has been purged. Close the valve immediately — turn clockwise until snug. Don't overtighten.
Check the boiler pressure
Bleeding radiators releases pressure from the system. Check your boiler pressure gauge — it should read between 1 and 1.5 bar. If it's dropped below 1, you need to repressurise the boiler using the filling loop.
Restart and test
Turn the heating back on and check that all bled radiators now heat evenly from top to bottom.

💡 Pro tip

Bleed all radiators once a year before winter. It takes 30 minutes for a whole house and keeps the system running at peak efficiency.

Expert tips for the best result

Always bleed radiators from the ground floor up — air rises, so top floors last
If air keeps returning, you may have a leak in the system drawing in fresh air — call a plumber
A boiler pressure below 0.5 bar means you need to add water via the filling loop before restarting
Bleed keys cost under £2 — keep one with your boiler manual
If water comes out immediately with no hissing, the radiator didn't need bleeding

Useful tools and products

Shop on Amazon → Screwfix → Toolstation →

When to call a professional plumber

If multiple radiators keep getting air pockets, if your boiler pressure constantly drops, or if you hear banging noises from the pipes — these suggest a leak or a failing component that needs a professional.

We connect you with vetted local plumbers across the UK — fast response, free quotes, guaranteed work.

💬 Get a free quote via WhatsApp

Frequently asked questions

How difficult is how to bleed a radiator for a beginner?

This guide is rated Easy. Bleeding a radiator removes trapped air that stops hot water circulating properly. If your radiator is cold at the top but warm at the bottom, it needs bleeding. It takes under 10 minutes and requires If you're not confident, a professional plumber can do this quickly and provide a guarantee on the work.

How long does how to bleed a radiator take?

Allow 5-10 minutes. This assumes the tools and materials are ready before you start. First-timers should budget extra time for preparation and any unexpected issues.

How much does a plumber charge for this in the UK?

Most plumbers charge £40-80 per hour depending on location and complexity. For a straightforward job like this, expect 1-2 hours of labour plus materials. Get a fixed quote via WhatsApp — message us with your postcode and job details.

How do I find a reliable plumber near me?

WhatsApp us with your postcode and job description. We match you with a vetted local plumber from our network — most jobs get a response within the hour. Contact us here.

How to bleed a radiator