How to Bleed a Radiator | Domestic & General

If you want to use less energy, and possibly cut your bills each month, then it’s worth looking after your heating system. Each part has a role to play — from your boiler to the pipes and radiators. Over time, small leaks and faulty valves can let air into radiators, which stops them heating up fully. We’ll tell you how to bleed a radiator quickly and safely, so you can feel the benefit of your heating again.

Prefer to watch?

Why do we need to bleed radiators?

Radiators are designed to be full of hot water from your boiler. If there’s a leaky pipe or faulty valve, water will drip out and be replaced by air. This leads to air pockets in the top of your radiators. And because air doesn’t carry heat as well as water, your radiators won’t get as warm as they should. This will also put strain on your boiler, as it will struggle to heat your home using less water.

How to check if your radiators need bleeding

Is the heating on, but your rooms aren’t as warm as they should be? Check for these signs that your radiators need bleeding:

The boiler pressure is too high (it should be 1 to 1.5 bar or 15 to 20 psi)
The radiators aren’t heating up properly
The radiators are colder at the top but warm at the bottom

You might also notice that the radiators take a long time to heat up, or they make gurgling noises.

Step-by-step guide to bleeding your radiators

First, identify which radiators need bleeding. Then figure out which radiator is farthest from the boiler, as that should be bled first. If your house has two or more stories, start with the radiators that need bleeding downstairs before doing any upstairs.

1. Find the tools you’ll need

You only need a couple of items to bleed a radiator:

An old cloth or jug to catch water
A radiator key or flathead screwdriver

You can get a radiator key from any hardware or DIY shop, and they cost about £2. There are a few different shapes and sizes, so take a photo of your radiator valve into the shop with you.

2. Let the radiators cool down

Before you start, turn off the heating and give the radiators time to cool down. Otherwise you could get very hot water on your hands.

3. Insert the radiator key and open the valve

Radiators have a bleed valve on one end, near the top. The part of the valve that you turn is a small metal square. It’s often inside a circle or hexagon of metal or plastic, depending on the radiator design. Insert the radiator key or flathead screwdriver into the valve. Turn it anti-clockwise until air starts coming out — you should hear a hissing sound.

4. Close the valve again

When water starts coming out of the valve, turn the key clockwise to close it again. Repeat steps three and four with all the radiators that need bleeding.

5. Turn the heating on and check the boiler pressure

Get your heating back up to temperature again and look at your boiler’s pressure gauge. It should be between 1 and 1.5 bar or 15 to 20 psi. To be sure, always check the exact details of your model in the manual. If the pressure is lower than 1 bar, you can increase it with the filling loop. For instructions on how to do this, see our boiler troubleshooting guide.

6. Test your radiators

When the heating is back on, see how the radiators have changed. Do they heat up faster? Are they warm all the way to the top? Do they no longer make gurgling noises? If so, it sounds like you’ve solved the problem.

How to bleed a radiator without a key

Radiator keys are handy, but you can bleed a radiator without one. You just need a flathead (slotted) screwdriver. Insert it into the slot in the radiator valve and turn it anti-clockwise to open, clockwise to close.

When to contact a heating expert

Have you followed these steps but your radiators still aren’t getting warm? There might be a problem with your boiler, or an unidentified leak in your heating system. First take a look at our advice on what to do if your boiler’s leaking. Then it might be time to call an engineer who’s qualified in boiler repairs.

About the author

Josh Allen

Josh is a copywriter at Domestic & General who works across our digital journeys and beyond. Starting out in journalism and travel writing 10 years ago, he's since turned his hand to technology and insurance. Josh is also a published short story writer with a novel in the works, and he's known to twang a tune on the guitar and banjo.