Enjoy FREE DELIVERY on most orders over £500!
Enjoy FREE DELIVERY on most orders over £500!
Skip to content
how to bleed a cast iron banner handy maintenance man fixing a radiator

How To Bleed a Cast Iron Radiator?

In this section, we will discuss how to bleed a cast iron radiator and also some useful guides and best practices to follow when bleeding a radiator. This article will help you give you informed guidance when completing such a task.

It is important to check the performance of your radiators as autumn approaches and winter nears. This includes checking and bleeding your radiators if necessary.

You may need to bleed radiators the next time you inspect your radiators or turn them on after those summer months where they have been laying idle.

A routine check after summer should be made procedure. All of this is to ensure your heating system is ready for winter.

So How do you bleed radiators?

The Urban Bathhouse will help you understand what the process is, and why it is so important.

cast iron radiator on the wall with man bleeding the radiator

What is a bled radiator?

The phrase "bleeding radiators" should actually read '“releasing trapped air” as this is actually what you are doing when we say “bleeding a radiator”.

It's possible that air bubbles were trapped in your radiators due to the fact you turned them off over summer.

The radiators will work more efficiently if you balance them and bleed them radiators. We will talk about balancing in a different post.

Bleeding or shall we say releasing trapped air, reduces the strain on your boiler, and can prevent costly issues. This can be done without a heating engineer, but you will need some old towels and something to catch the water this is where the term "bleeding" comes from this.

How to Bleed a Cast Iron Radiator in 9 Easy Steps

To avoid any hassle, follow these 9 step simple instructions.

1) Gather Supplies: Gather the tools you will need, such as a screwdriver or radiator bleed key, a towel or cloth, and a container for any water discharge.

2) Switch off Your Heating System: This will prevent hot water from flowing through the radiator while the bleeding is being done.

3) Bleed Valve - locate this: Identify the bleeding valve on your radiator made of cast iron. The bleed valve is usually located at one of the corners, and looks like a hexagonal or square bolt. Place a towel, cloth under this valve to catch any drips.

4) Insert Bleed Key: Turn the valve in a counter clockwise direction using a radiator bleed tool or a screwdriver. Avoid damaging the valve by applying even, steady pressure.

5) Listen for Hissing Sound: Listen for a hissing noise as you turn the bleeding valve. This sound indicates that trapped air has been released from the radiator. Continue turning the radiator until you see water dripping out.

6) Collect water in container: Under the bleed valve, place the small container to catch the water. This will prevent water from dripping on the floor.

7) Close the Valve: Close the bleed valve clockwise once the hissing has stopped and the water is flowing consistently. Avoid damaging the valve by not overtightening.

8) Check Pressure: Check that the pressure in the system is within the range recommended. Consult your manual to learn how to adjust the pressure if necessary.

9) Turn on you heating system: Monitor the performance of the radiator after bleeding it. To confirm that trapped air has been removed, check for an even heat.

Why do you need to bleed radiators?

Most radiators require bleeding at some point in their lifespan.

The air trapped in your radiators can make them less efficient by preventing them from heating to their full potential.

Bleeding radiators will ensure that your heating system is working to its full potential and that you're not wasting energy. It is best to balance your radiators and bleed them at the same time.

After checking your heating, you can do this. After 30 minutes, turn up the heat and check that all radiators are warm. Rebalance your radiators if they are hot only at the top, bottom or if some take longer to heat up than others.

handyman bleeding a cast iron radiator

Cold Radiators? Do I need to Bleed Them? - 5 checks to make

When the weather turns cold, especially in winter and autumn, nothing beats coming home or waking up to a warm home.

If your radiator remains cold even after you have turned on your heating, you might need help.

Radiators that do not warm up or fail to heat up at all may also be a sign of larger problems. This could include debris in the system blocking it or an improper system setup. We've listed below some reasons why a radiator might be cold.

1. Boiler

Make sure your heating is set correctly and that it works properly. Check to see if your boiler has a fault code. If you have a fault code, it may be more difficult to fix.

2. Pump

Check that your heat pump is working. If your heat pump stops working, the water that is used to warm up the radiators will not be heated. This can cause all of the radiators to lose temperature. If you hear any noise, it is the easiest way to determine if your heat pump is functioning.

3. Air in the System

It is possible that there is air in your heating system if you notice one or more radiators are cold when the heat comes on. The air in your heating system tends to collect at higher points, preventing the water from being distributed. This is why you will only feel the warmth of the radiator's bottom.

4. Valves stuck

A stuck valve can cause a cold radiator. If the problem only affects one radiator, this is often the case. It is possible that the thermostatic valve (the white one) which controls the water flow can get seized up due to age or inactivity.

5. Water pressure

Your water pressure could be too low if your boiler and pump work. Normal pressure should be between 1.5 and 2 bars. You can see this on your gauge, and it may be necessary to adjust the system.

Arroll Luxury Radiator Bleeder Valve Air Vent on radiator

How often should you bleed radiators?

Radiators should be bled as soon as a problem is noticed.

It will ensure that your heating system runs as efficiently as it can and that you don't waste money on energy which isn't being converted into heat.

It is best to check that they are heating up correctly in the summer and early autumn, when temperatures are higher and engineers are not as busy.

If you feel you need to, bleed the radiators to ensure you are ready for winter. It's a good idea to establish a quick annual check, just before autumn and winter is upon us.

How long should you bleed your radiator?

It is not necessary to wait a specific amount of time before bleeding your radiator.

Most will need to be bled until the hissing noise of air escaping stops.

Water should leak out slowly, without any air bubbles. The length of time it takes to do this depends on how big your radiator is.

It could take anywhere between a few minutes or a couple of seconds.

Looking for a Radiator Bleed Valve?

Please check out our radiator bleed valves here - click here

cast iron radiator on the wall within a living room

Bleeding Radiators - Frequently Asked Questions

Have more questions on how to bleed your radiators? No worries, check out our useful FAQ section below for more information.

How do I know when my radiator needs bleeding?

You may notice that your radiator needs to be bled if you see any of the following signs:

  • Uneven Heat - Usually hot at the bottom and cold at the top
  • Heat up takes longer than normal
  • When heating up, you may hear a gurgling sound
  • When you turn on the central heating, pipes will bang.

If you see, hear or feel any of these symptoms, try bleeding the radiators first. If bleeding does not help, then there could be another problem.

Do You Bleed The Water Out Of A Radiator?

You should not bleed the entire water out of your radiator. Bleeding your radiator's main purpose is to remove air. Close the valve immediately when the water begins to leak without bubbles.

What to do if no water comes out when bleeding a radiator?

There could be a problem with your radiator if you need to bleed it frequently, and there is no water coming out. You may need to balance the radiators if you're sure that your boiler pressure is not too low.

Call a plumber for advice, or perhaps it's time to replace your radiator with a nice new one. You can ask a plumber to help you or replace the radiator.

What Radiators should you bleed first?

Start by bleeding the radiator furthest from the boiler, and work your way backwards. Preferably start at the ground floor and work upwards to the first floor.

How do you bleed a radiator without a key?

You will need one most of the time. If you've lost it, you can find a new one at any DIY or hardware shop. Radiator keys are often easier to use than a flathead screwdriver.

Can you bleed a radiator when the heating is on?

You don't want any boiling water to shoot out at you, so NO do not bleed radiators whilst the heating is on.

Also when the heating is off this makes it easier to bleed radiators, since the water has settled at the bottom.

Turn on your heating at least two hours before you plan to bleed your radiators. It will allow the pressure inside to build and you can identify which radiators have a problem. Turn it off, and wait for them to cool down before you begin the bleeding procedure.

Does Bleeding Radiators Reduce Boiler Pressure?

You can lower boiler pressure by bleeding your radiators. This is because you've released some water from the system. It is easy to fix this problem - simply top up your boiler's pressure with the filling hose.

You may find that your radiators remain cold if you don't restore your boiler pressure to the recommended setting (usually between 1.5 and 2.0 bars). If your boiler pressure is normal but your radiators remain cold, repeat the bleed procedure a second time.

Previous article Are Cast Iron Radiators Efficient?
Next article Do Metal Baths Lose Heat Quickly?