If your radiator’s feeling a bit patchy, trapped air is usually the party crasher. Bleeding your radiators lets that stubborn air escape, so heat can flow freely once more. The payoff? Faster warm-ups, better efficiency and a home that feels properly snug - without cranking up the bills. This step-by-step guide shows you exactly how to bleed a radiator safely and correctly.
What you'll need:
- One radiator key
- Two rags (the older, the better)
- One small container to catch any drips
Step summary
Turn heating on → Check for cold spots → Turn heating off → Fit the key → Release the air → Close the valve → Repeat around the home → Check boiler pressure.
Step 1. Turn your heating on
Pop your heating on and let your radiators warm all the way up. This builds pressure in the system and makes it easier to spot which ones need a little TLC.
Step 2 – Check radiators
Gently feel for cold patches, usually lurking at the top. If a radiator takes forever to heat up or feels warm at the bottom but cool above, trapped air is likely the culprit.
Hot tip: Radiators really do mean business when they’re on - handle with care.
Step 3 – Turn your heating off
Before you reach for the key, turn the heating off. This keeps things calm, controlled and splash-free. Hot water on the floor is never part of the plan.
Step 4 – Fit your key to the bleed valve
Find the small bleed valve at the top of the radiator — a tiny square pin inside a round nut. Slot your radiator key on and you’re ready for action.
Step 5 – Open the bleed valve
Slowly turn the key anti-clockwise. You’ll hear a soft hiss as the trapped air escapes. That’s the sound of progress. Keep going until the hissing stops.
Step 6 – Close the bleed valve
Once the air is gone, tighten the valve straight away. Water won’t be far behind, and modern valves can be a little… enthusiastic. Keep your container and rags close.
Step 7 – Repeat for all radiators
Work from the lowest radiator in your home and move upwards. Air rises, so this bottom-to-top approach helps clear the whole system properly.
Step 8 – Check the boiler pressure
When you’re done, check the pressure on your boiler.
If it’s where it should be - lovely job. Turn the heating back on.
If it’s low, you’ll need to top it up using the filling loop.
Always follow your boiler manufacturer’s instructions. If anything feels unclear, a qualified engineer is your best bet.
Do I need to bleed my heated towel rail?
Yes - if it’s part of your central heating system, a heated towel rail can trap air just like a radiator. If it’s warm at the bottom but cool at the top, bleeding it will help restore even heat and keep it working efficiently.
Electric-only towel rails don’t need bleeding.
Sorted?
If your radiators are now heating evenly from top to bottom, you’ve nailed it. For best results (and consistently cosy toes), give your radiators a bleed about once a year.
If the cold persists…
If one stubborn radiator still feels chilly, simply turn the heating off and repeat the process as some air pockets need a second gentle nudge.
And if it still won’t budge, there may be a build-up of rust and debris inside the system (known delightfully as ‘sludge’). At that point, you’ll either need a professional power flush by a heating professional, or check out our guide on how to flush sludge from your radiators yourself if you’re feeling brave.
