How to bleed a radiator?

Does my radiator need bleeding?

Is your home not heating up as much as you’d like? Have you turned up your thermostat higher than you normally would? There’s a good chance that your radiators are not as efficient as they could be. A common cause of this is air trapped inside the heating system – and this is when to bleed your radiators.

Your central heating might also be making noises: trapped air causes gurgling, clanking and banging noises in your pipes. We’ll show you how to bleed a radiator without a key, but it’s best that you have one to hand.

What does bleeding a radiator mean?

Bleeding a radiator is the act of removing trapped air from the inside of your radiator or any heating appliance connected to your central heating (like a towel rail in the bathroom, for instance).

Trapped air stops heat reaching all parts of your radiator, making your central heating system less effective. It takes longer to warm up rooms and the lost efficiency means you’ll pay higher bills.

Checklist: when to bleed radiators

The quickest way to check if your radiators need bleeding is to check for cool spots on your radiator. Simply turn your heating on and leave it to warm your radiators fully. This should take around 15 minutes or more, depending on how big your home is and how old your heating system is.

Once your radiators are at their peak warmth, check each one in your home for cool areas. Be careful: your radiators might be hot. If you need to, wear thin gloves to avoid burning yourself. Be safe: don’t leave any part of your hand on the radiator for longer than a second.

If you’re noticing cool spots at the top of any of the radiators (particularly the ones higher up in your home), then this is when to bleed your radiators. If the cool spots are at the bottom, then check our in-depth article on what to do if your radiators are cold at the bottom.

How to bleed a radiator

You’ll need an old towel or rag and a radiator key (some radiators require a screwdriver). You can get one for cheap online or at your local DIY store. We recommend you purchase a radiator key if your radiator needs it, but if you don’t, we’ll show you how to bleed radiator without a key below. If you have a key, here are the steps:

1. Switch off your central heating (allowing radiators to cool).
2. Have your old towel ready (to catch any water splashing out).
3. Using the radiator key (or screwdriver), gently loosen the valve at the top of your radiator.
4. Twist slowly until you hear a hiss. The more air in your radiator, the more pronounced the hiss.
5. When the hissing slows, water might start to dribble out (or gush, if you’ve loosened the valve too much – this is why we have a towel handy!).
6. Tighten up the valve immediately.

Congratulations, you now know how to bleed a radiator. Your radiator should no longer be cold at the top, and your home should warm up faster and more efficiently. You’ve probably saved on your heating bill, too!

Depending on the amount of air that came out, bleeding your radiator could have lowered your boiler pressure. You might want to check your water pressure. Good boiler pressure needs to be between the 1 and 1.5 bar on the pressure gauge. That’s the happy zone for boilers.

How to bleed a radiator without a key

If your radiator doesn’t need a key

Some radiators don’t require a key in order to bleed them. For these, you’ll most likely need a screwdriver with the correct head shape. Check your radiator (and any user guides if you have them) to make sure you have the correct screwdriver. Never use a wrong-shaped screwdriver head! It could damage the radiator by stripping the metal of the screw, preventing you from loosening or tightening it in the future.

If your radiator requires a key

If you want to know how to bleed a radiator without a key, then you can use a flat-headed screwdriver if it has a small slit in the middle. Don’t use a cross-headed (Phillips) screwdriver or pliers: these can damage the radiator valve.

If your radiator doesn’t have a slot that can be used with a screwdriver, we recommend you get your hands on a radiator key. They’re very cheap, and can be bought online or from most DIY/hardware shops or plumbing merchants.

It’s worth getting the right tools for the job, especially when they’re easily available. Otherwise, you might end up with a damaged radiator, which will cost a lot more to fix or replace!