How to bleed a radiator

boiler-Installation London
boiler installer London

Our expert engineer with years of experience in the industry will guide you through how to bleed a radiator in your home avoid corrosion and save money on energy bills and heating bills.

Check your heating system every few months if needs bleeding radiators. Installing a magnetic filter and pouring inhibitors in the system can decrease corrosion and unwanted air buildup in the heating system.

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Why do you need to bleed a radiator?

Bleeding radiators will help the boiler and the heating system perform better. It’s a very common boiler problem even in an unvented heating system when you have a heat-only boiler.

All the trapped air in the system creates cold spots and the radiators stop the water circulation. Also, a lot of air in the system can cause central heating pump cavitation, which will lead to pump failure. Trapped air escaping water inside the system can cause corrosion too.

The Radiator at the top is cold

For us engineers, it is easy to check with a thermal camera what is the issue.

The most common sign when it’s time to bleed radiators is when the top side of the average radiator is cold. The air trapped inside the top of the radiator stops the heating system’s water circulation and also shows cold spots on the radiators.

To bleed out the radiator is very easy, but you have to be careful not to splash the dirty water everywhere. If you release the air from the system and you don’t have any other issues, your heating system will work again.

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The whole radiator is cold

This is very cold weather not a common sign of air in the system. If the entire radiator is cold, you could have problems with the central heating circulation.

Here are the reasons why the entire radiator is cold:

  • You can have sludge build up in the bottom of the radiator, blocking the water flow.
  • Your thermostatic radiator valves are faulty or blocked and no flow will come through the radiator.
  • You could have a faulty central heating pump or diverter valve depending on what boiler and system you have.
  • It can be heating system faults that are not opening the diverter, or motorized valves.
  • If your system doesn’t have a magnetic filter, high corrosion can lead to underperformed radiators.

As you see many faulty parts can cause radiator blockage.

If you are struggling to find a solution for your heating system repair, find an engineer who will help you resolve your problem.

Radiator rattling noise

Trapped air in the heating system can cause your radiator to rattle and give out gurgling noises. Your pipework can be noisy too. All you have to do is bleed out the and bleeding your radiators and you might sort out the issues.

Tools you need to bleed out the radiators

  • Radiator key
  • Sometimes a flathead screwdriver.
  • A pipe wrench, to hold that bleed valve if it’s turning.
  • An old towel or toilet paper or a bucket to catch the water.
  • Gloves, sometimes there is dirty water in the radiators.

Top tips: Don’t burn yourself! If you heat the system the water in the radiator can be more than 60 degrees.

Steps to bleed the radiators

Follow our step-by-step guide to bleed out your radiators and avoid mistakes.

Before you start the work, don’t forget to open the radiator thermostatic valves and lockshield valves. Also, take off the thermostatic valve head and check the valve pin if it isn’t stuck. If the pin is stuck, you can get a spanner and try to pull up 1-2 millimetres. Don’t pull out the pin too much because if it comes out, you end up with a fountain in the bedroom.

This pin is controlling the flow into the radiators.

We normally just push down the pin, and if it’s moving easily then it’s working properly.

Key tips: When you bleed radiators, the boiler pressure will drop (if you have a sealed combi or system boiler). All you have to do is to start to top up the system to 1 bar when it’s dropped. When you fill your system, do it slowly to avoid too much water leakage or too much air getting in the system. With cold water, you also introduce more air to the radiators.

The open-vented system will top up automatically.

Bleeding a radiator when it’s cold

First, bleed your radiators when they are cold. Start with the downstairs radiators first. If the radiator bleed valve is turning while you open the small pin, you have to hold the valve with a pipe wrench.

Turn your heating on

After you heat your central heating system, again you start at the downstairs radiators. When the water begins the central heating system is warm the air from the cold water will dissipate. Also, the hot water will expand, creating pressure in the system and it will help bleed the radiators.

Check which radiators need bleeding

Identify the cold spot patches on the radiators. But we recommend bleeding out all your radiators in your home!

Switch off your central heating system

You turn off your heating system to avoid too much hot water from coming out from the radiators. Also, you can avoid the central heating pump running dry causing cavitation.

Before you start bleeding the radiators

Get a towel and a small bucket under the bleed valve. Put it very close to the bleed valve so not one drop of dirty water can go onto your white carpet. Also, think about emergencies! If your bleed valve came off, get ready to close both sides of the radiator valves.

Open the radiator bleed valve with a bleed key

Put the radiator bleed key (or flat-head screwdriver) into the bleed valve. The pin that you have to turn is a small square nipple (screw). You have to slowly turn the bleed valve anticlockwise and release the air escaping from the system. Sometimes when air escapes it comes out smelly, this is a sign of corrosion in the system. You can smell the hydrogen buildup in the radiators, which is a product of corrosion.

Hold open the bleed valve

Just open the valve slowly turning it anticlockwise over and tightening over till you hear the hissing sound. Do not turn the pin fully out, anyway, all the water will go to the floor beneath. There is high water pressure in the radiators, if the pin comes out it will be hard to put it back.

Hold the valve open till the water releases air to come out from all the radiators. Now you completed the radiator bleeding. Turn back the radiator screw but don’t overtighten. Now all the air is released from the system and you can go to the other radiator.

Top up the pressure in the central heating system

After you finish the first bleed your radiator is bleeding, and you have to top up the pressure in the system.

First, you have to find the pressure gauge, which can be on the boiler or next to the square inside the expansion tank, if you have a vented system.

The boiler pressure needs to be 1-1.2 Bar. You find the filling loop in the combi boiler, which is a flexible pipe with both ends an isolation valve. You have to fully open both valves slowly and start to top up the system. If you over-pressurise the system, you just go to one of the radiators and bleed out the water. This will decrease the pressure in the system.

How to run your system energy efficiently

Keeping the system clean by installing a magnetic filter, and also using an inhibitor for system protection. You can book a central heating system wash and also upgrade your radiator valves for a newer one. All these steps make sure you have a fully working energy-efficient heating system.

Don’t run the radiators at number 5 (in the radiator thermostatic valve) in the room that you are not using and save money on your energy bills.

Just to know bleeding a radiator doesn’t mean you cleaning the heating system. If you need a system clean, you need to book a power flush or system clean wash. For cleaning, the central heating system needs to be drained, filled and washed properly and inspect all the other radiators, one by one.

Hope all of the above information will help you to diagnose what is the issue in your heating system.

Did you manage to bleed out all your radiators? Are they still cold? For fault diagnosis, you can contact MML Plumbing and we can book you a fully registered gas-safe engineer who can fix your radiator problems!

Do you need a heating engineer?

If you need a heating engineer who can fix your heating problem, contact us today in North London and we will book you a professional plumber or gas engineer.

Frequently asked questions about bleeding a radiator

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