how to replace a radiator

How to Replace a Radiator Easily Like a Pro

Knowing how to replace a radiator is a skill that can save you a lot of money. As a heating engineer, I have replaced a lot of radiators in over ten years of plumbing.

What I can tell you from all those radiator replacement jobs is that every job is different – some are easy, some are hard. Whether you need to how to remove a radiator for decorating, or how to replace a radiator valve, I can teach you.

If you are replacing a radiator because it is not working, you could have an airlock, or a radiator valve problem, or you might need to balance the radiators. But if it’s leaking, rusted, or just old and inefficient, then replacing the radiator is what will need doing.

How to Replace a Radiator – the Easiest Way

If you want to know how to replace a radiator the easiest way possible, then buying the exact same radiator is the way to go. The same make, the same model, the same size. This way you can change the radiator without draining the system.

You can use the same radiator brackets that are already fitted to your wall for the old radiator. Just remove the old radiator by undoing a couple of nuts on the radiator valves and hanging the new radiator straight on.

How to Remove a Radiator Without Draining the System

Knowing how to remove a radiator without draining the system is the best way to remove a radiator. Draining the central heating system and refilling can take a long time and sometimes cause problems depending on the system.

Whether you are removing it for decorating or replacing the radiator for one of the same length, it doesn’t get any easier than removing the radiator without draining the system. You will need two people to do this unless it’s a small radiator.

  1. Close both of the radiator valves on the radiator.
  2. Place some old towels under the radiator valves to catch any dirty water.
  3. Crack the nuts with an adjustable spanner in between the radiator and radiator valves.
  4. Let the water drop onto the towels until it stops coming out. If it doesn’t stop coming out, you will need to drain the system, as the valves are probably broken.
  5. Pull the valves off the radiator tails and place your thumbs over the tails to stop the water from coming out of the radiator. If you can’t reach both tails, you will need someone to help.
  6. Then remove the radiator by lifting it off the brackets and empty the water down a drain or a toilet.

How to Change a Radiator Without Draining the System

If you managed to buy the exact same radiator to replace, then you can change it without draining the system. Remove the old radiator as above, then fit the new radiator valve tails on the new radiator, or you can use the tales from the old radiator.

You need to wrap plenty of PTFE tape around both tail threads (I normally do at least 15 wraps) before screwing it into the new radiator, and then tighten it up with an adjustable spanner or Allen key. It should be really stiff to turn the spanner on the last couple of turns.

If it’s not, then remove the tail and remove the PTFE tape. Then start again using more PTFE tape than before and screw it back into the radiator. Keep doing this until is nice and tight. If it’s not tight, then it will probably leak.

Fit the new radiator bleed valve and blank plug that should have come with the new radiator, and tighten them up with an adjustable spanner.

Replacing a Radiator

  • Hang the new radiator (with tails fitted) on the old brackets
  • Connect the old radiator valves onto the new radiator tails with new nuts and olives
  • Open both radiator valves
  • Bleed the radiator
  • Top the pressure up

This is the easiest way to change a radiator or remove a radiator for decorating if you are refitting the old one.

How to Replace a Radiator With a Smaller One

Replacing a radiator with a smaller one is much more difficult. You will have to fit the new brackets for the new radiator, which will always be in a different place. Yeah, it’s only a few screws, but it’s getting the correct height measurements to fit the old pipes that is the tricky part.

Replacing a radiator with a smaller one is the most common radiator replacement I do when a different size is needed. This is because the smaller one is usually only a tiny bit smaller when replacing an old Imperial-sized radiator.

But, occasionally it will be a larger one needed. In this case, the pipes will definitely need to be adapted to fit the larger radiator, which is much more difficult than replacing with a slightly smaller one.

How to Measure a Radiator

Learning how to measure a radiator is very simple. No need to overthink this. To measure a radiator, grab your tape measure, and run it along the top of the radiator from one edge to the other. This is the length.

To measure the height of the radiator, hold the tape measure on the bottom edge of the radiator and run it to the top edge and note down the numbers.

Imperial vs Metric

Old imperial-sized radiators are measured in imperial inches, new radiators are measured in metric millimetres. It’s very common to replace an imperial radiator with a metric radiator.

The problem with this is you can’t always get the same size radiator when changing radiators. There are websites out there that sell the old imperial sizes, but you could pay £400 for a radiator that would be £100 for the closest metric size.

You might have to buy a metric one that is slightly shorter or slightly longer. Height doesn’t really matter, it’s all about the length to fit the pipes. I always go slightly smaller. This way I can use longer radiator valve tails.

Radiator Valve Tails

You can get 100 mm long radiator valve tail extensions (or shorter ones) and cut them down with a standard pipe slice, or with a hacksaw, to the length you need.

radiator valve tail extension
A 100 mm radiator tail extension.

These are what I use most of the time and always have at least a couple on the van, but you can get other types of tail extensions that might suit your radiator or valve better.

It won’t always be possible to use tail extensions because of larger size differences if you need a much larger radiator, you might need to adapt the old radiator pipes to fit the new radiator.

This is not an easy part of changing radiators, as you will probably have to pull the floor up to access the pipes. You can adapt the pipes above the floor but it won’t look as neat. Just make sure you measure the radiators accurately.

How to Fit a New Radiator

To fit the new smaller radiator onto the old valves with long tail extensions, here is my process.

This applies to standard panel radiators only. Column radiators, and other types, are totally different to fit.

Stand the new radiator against the wall exactly where it’s going in between the pipes. Then mark the wall with a pencil in the centre of the brackets attached to the new radiator. This is where the new wall brackets will go.


For the height of the new brackets on the wall, you will need to take some measurements. First, measure the height from the floor to the centre of the old radiator valve pipe hole.

Then, measure from the bottom of the fixed bracket on the new radiator to the centre of the radiator valve hole on the radiator. This can be tricky. Add these two measurements together, and then mark the wall in line with one of the other pencil marks you made.

This is where the bottom of the radiator bracket will sit, not the bracket that gets fixed to the wall, but the bottom of the bracket on the radiator.

Fit Wall Brackets for the New Radiator

Once you have this marked correctly, hold the wall bracket against the wall and use a pencil to mark all the screw holes. Then you can drill and plug the wall and fit the first wall bracket. Use a sprit level to mark the height of the other wall bracket, then fit that one.

Fit the New Radiator

Now time to fit the new radiator on the brackets, just lift it onto the brackets and mark the long tails where they will sit inside the old valves and remove the radiator. Then cut down the tails, using a 15 mm pipe slice is a much better option, but a hacksaw will do the job.

Rehang the radiator onto the brackets and the tales should now line up to the old valves on the pipes, you will need some new 15 mm nuts and olives which you can tighten up with a spanner.

Make sure you fit the radiator bleed valve on the new radiator, and blanking cap on the opposite side, then open both radiator valves, top the pressure up at the boiler, bleed the radiator and check all the other radiators for air with the bleed key.

Repressurise the boiler again if needed and turn the heating on to make sure the new radiator is working and there are no leaks. That is how to fit a new radiator.

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