How to Bleed a Radiator?

Now that the temperature is falling, you may have cranked up the heat in your house only to find that one (or more) of your hot-water radiators remains cold. If a single radiator isn’t generating heat when the rest of your system seems to be working fine, your problem may be air trapped inside the radiator a common issue with hot-water heating.

Before you call the plumber, try your hand at solving the problem yourself by bleeding the radiator. It takes just a few simple steps, and the tools required are minimal. Give it a shot! You’ll have the place all warmed up in no time.

This guide will show you how to bleed a radiator in seven simple steps, helping you combat cold rads and improve your home’s heating efficiency.

When to bleed radiators?

If your radiator is cold at the top but hot at the bottom, then there’s likely to be air trapped inside and you may need to bleed it. Here are some other tell-tale signs that your radiator needs bleeding:

Radiator cold at the top

This is the most common sign that your radiator needs bleeding, which essentially means air has collected in the radiator, stopping the hot water from circulating around and heating it up. The air needs to be released so your radiator can heat up effectively. Patchy warmth in your rad is definitely a sign it needs to be checked out before it stops heating up altogether.

The entire radiator is cold

Though this isn’t as common a sign that radiators have air trapped in them, it certainly is a sign that your radiator needs attention. Trapped air somewhere in the pipes has restricted the hot water which is meant to be flowing into the radiator – this can cause bigger problems later if it’s not sorted quickly! You should get in touch with your local heating engineer to get things toasty again.

Mold or damp around the house

If you’ve noticed grubby damp patches or mold sneaking in on the walls, particularly in rooms that aren’t used very often, this could be a sign your radiators need some attention.

Radiators are rattling

Trapped air in your heating system may cause your radiators to make funny noises, like gulping, gurgling, and rattling. Whilst this could be for various reasons, it may be a sign that you need to bleed the radiator. Either way, your rad needs to get checked to make sure the problem isn’t more sinister.

What You’ll Need to Bleed a Radiator

The tools you’ll need are simple. Many bleed valves require just a straight screwdriver to operate. Make sure yours is properly sized though.

Using too small a screwdriver can wear the slot to the point that you won’t be able to turn the screw, and then you’ll need to call the plumber. Older radiators may require a radiator key. These come in several sizes, and selections are available at old-fashioned hardware stores, home improvement stores, and plumbing supply houses.

How to Bleed a Radiator in 7 simple steps

Follow this simple step-by-step guide to check and bleed your radiators:

1. Turn your heating on

Turn your heating on and wait for all of the radiators in your home to warm up (the length of time may depend on how many radiators you have and the size of your home, so be sure to give yourself plenty of time).

2. Identify which radiators need bleeding

Carefully check each radiator to ensure it has an even temperature across the whole surface area. If you do find any radiators that are cold at the top or hear any gurgling noises, it’s a good indicator that there’s trapped air inside and that you’ll need to bleed it.

Tip: We recommend wearing a thin pair of gloves when checking each radiator as they may be very hot.

3. Turn off you’re heating and wait for the radiators to cool

Before you start bleeding any radiators, we recommend turning off your heating so the radiators aren’t too hot to touch

4. Place a cloth below the radiator bleed valve

Locate the radiator bleed valve and ensure that a cloth or an old towel is placed below it to catch any water that may be released.

How to Bleed a Radiator

Tip: Every radiator has a bleed valve. They’re typically located at the top corner of a radiator and look like a round hole with a square inside.

5. Open the valve and release the air

If no water or air comes out when you bleed the radiator, then the valve could be blocked with paint. Close the inlet and outlet valve at each end of the radiator, then remove the screw from the centre of the bleed valve. Insert the radiator key into the bleed valve and slowly turn it anti-clockwise (a quarter of a turn should be enough). You should hear a hissing sound as the air escapes.

Tip: We recommend having a bucket handy to catch any spurting water, just in case you open the valve too far.

6. Close the valve

Once the hissing sound stops and water starts to leak out, turn the key clockwise to close the valve.

7. Check the boiler pressure

Repeat this process for each radiator that needs bleeding in your home. Once you’ve finished doing this, you’ll need to check the pressure of your boiler’s water pressure gauge.

If the boiler pressure is too low (below 1 bar), you’ll need to repressurize the system. If the pressure is normal (between 1 and 2 bars), you can switch your heating on and check that your radiators are now heating up as they should.

How Does Air Get into a Hot Water System?

How does air get into a closed plumbing system? In some cases, it’s not air at all. If your pipes are a mix of iron and copper or brass, galvanic corrosion may be releasing hydrogen gas.

Or, you might have an older pressure relief tank, which relies on a pillow of air to prevent dangerous pressure from building up in the heating system. Cooler water dissolves some of the air, and when the system kicks on, the heat drives the gas out of solution.

Modern pressure tanks separate the water from the air with a rubber bladder. Old steam systems can actually suck air in. As the steam cools, it shrinks dramatically, causing a partial vacuum.

You can eliminate or reduce the buildup of air and other gasses in your system by being sure there’s an air eliminator installed just after the boiler. This is a job for a plumber.