Bleed all radiators
Save £80–150 in 1 hour — no heating engineer needed
Most people call a heating engineer for this. You probably don't need to.
Last updated: March 2025
Only basic tools needed — most homes already have them.
Before you start
Bleeding all radiators is worth doing at the start of every heating season — typically October. Air enters the system over summer and accumulates in the top of radiators, reducing their heat output and making the boiler work harder.
You need one tool: a radiator bleed key. Have a cloth and a bowl for each radiator — some release more water than others, especially if they haven't been bled in years.
Some links on this page are affiliate links. If you buy through them we may earn a small commission at no extra cost to you.
Tools & materials
- !Radiator bleed key— buy from any hardware shop or DIY store
- ✓Old cloths or towels— one per radiator to catch drips
- ✓Small bowl or container— to catch water if significant air has built up
Want everything in one go?
Prices shown on retailer sites. Always check current pricing before purchasing.
Turn the heating on and identify cold radiators
Run the heating for 20 minutes, then feel the top and bottom of every radiator. If the top is cold but the bottom is warm, trapped air is blocking circulation — it needs bleeding. Note which radiators need attention.
Most people get this done in under 5 minutes.
Where beginners go wrong
Bleeding in the wrong order — always ground floor first, furthest from boiler first, then work up and towards the boiler.
Not checking boiler pressure during the process — pressure can drop significantly when bleeding multiple radiators in sequence.
Opening the valve too far — a quarter-turn is all that is needed. Too far and water gushes out, making a mess and dropping pressure fast.
Stop and call a heating engineer if...
Radiators remain cold at the bottom after bleeding — this is sludge, not air, and requires a power flush
Black, oily, or very dirty water comes out when bleeding — indicates severe corrosion in the system
Boiler pressure drops to zero within 24 hours of repressurising — there is a leak
Cost breakdown
Recommended starter kit
Five tools that cover most home repairs.
- →Adjustable spannerAmazon·Screwfix
- →Screwdriver setAmazon·Screwfix
- →PTFE tapeAmazon·Screwfix
- →Spirit levelAmazon·Screwfix
- →Tape measureAmazon·Screwfix
Want everything in one go? Get it on Amazon
What you just learned
You now know how to maintain your whole central heating system annually. Regular bleeding keeps your system efficient, reduces gas consumption, and extends boiler life.
Most people would pay a tradesperson for this.