How to Change a Radiator: A Step-by-Step Help Guide

Last updated on February 22nd, 2024

A radiator not working, leaking, rusting, or maybe you just want a newer or more powerful one, are a few reasons for changing a radiator.

This is a job that can be easy or a nightmare as each job and setup is different.

I have been a full-time heating engineer changing radiators for over a decade and have replaced many radiators.

How to Replace a Radiator With The Same One

If you want to know how to change a radiator the easiest way possible, buying the exact same one is the way to go. The same make, same model, same size.

This way you can change the radiator without draining the central heating system.

Use the Old Wall Brackets

You can use the same wall brackets that are already fitted to your wall for the old radiator.

Just remove the old one by undoing a couple of nuts on the thermostatic radiator valve or lockshield valves and hang the new radiator straight on.

How to Remove a Radiator

The first thing to do when you are replacing a radiator is to remove the old one.

To remove a radiator you should drain the central heating system.

You can remove a radiator without draining the system but you won’t be able to replace the thermostatic radiator valves or lockshield valve.

1. Undo the nuts on the valves with an adjustable spanner
2. Disconnect the radiator valves if you are replacing them
3. Lift the radiator off the brackets on the wall

Replacing a Radiator Without Draining the System

If you managed to buy the exact same radiator to replace, you can change it without draining the system:

1. Put some old towels under the radiator valves
2. Close both valves fully
3. Put a plumb tub under a radiator valve
4. Crack the nut in between the valve and the radiator
5. Let the water out slowly into the plumb tub
6. Keep emptying the plumb tub until the water stops coming out
7. Undo the nuts on both valves fully
8. Lift the radiator off the wall brackets
9. Take the old tails out of the old radiator and fit them on the new one with at least 15 wraps of PTFE tape
10. Hang the new radiator on the old wall brackets
11. Connect the tail nuts to the old valves and tighten them up with an adjustable spanner
12. Fit the new bleed valve and blank nut that come with the new radiator
13. Open both valves
14. Bleed the radiator with a radiator bleed key from the radiator bleed valve
15. Repressurise the boiler
16. Turn the heating on and test the radiator

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 replacement job 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 need to be adapted to fit the larger one, which is much more difficult than replacing it 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, hold the tape measure on the bottom edge of the radiator and run it to the top edge and note down the measurements.

Replacing Old Radiators With New Sizes

Old imperial-sized radiators are measured in imperial inches, new ones are measured in metric millimetres.

It’s very common to change an old imperial radiator with a new metric one.

The problem with this is you can’t always get the same size when changing radiators.

There are websites out there that sell the old imperial sizes, but you could pay £400 for a radiator which 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 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 60mm long radiator valve tail extensions (or longer ones) and cut them down with a standard pipe slice, or with a hacksaw, to the length you need.

These are what I use most of the time and always have at least a couple on the van which can be fitted easily with a radiator spanner key.

Adapt the Pipes

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 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. Make sure you measure them accurately.

How to Fit a New Radiator

Here is my process to fit the new radiator:

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.

Measuring

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 new tail.

This can be tricky. Add these two measurements together, and then mark the wall in line with (below) one of the other pencil marks you made.

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

Fit The New Wall Brackets

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 spirit level to mark the height of the other wall bracket in line with the other pencil mark, then fit that one.

Fit the New Radiator

Now time to fit the new radiator on the wall brackets:

1. Lift the radiator onto the brackets
2. Mark the long tails where they will sit inside the old valves with a marker
3. Lift it off the brackets
4. Cut down the tails using a 15 mm pipe slice (or a hacksaw will do the job)
5. Rehang the radiator onto the brackets
6. Fit new 15 mm nuts and olives on the tails
7. Fit the radiator valves onto the tails and tighten the nuts up with a spanner
8. Fit the bleed valve and blanking cap on the opposite side and tighten with a spanner
9. open both valves,
10. Bleed the radiator and repressurise the boiler
11. Check all the other radiators for air with the radiator bleed key
12. Repressurise the boiler again if needed and bleed all the radiators
13. 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.

The radiator replacement job in the photos was changed with the same-sized radiator. I also replaced the valves as I do with all radiator replacements.

Make sure to fit the new radiator bleed valve and blank nut that come with new radiators. More details here: how to replace a radiator bleed valve.

Conclusion

Learning to change a radiator can be a daunting task and should ideally be done with two people and a decent adjustable spanner.

If you can find the exact same radiator that you are replacing that is the easiest and best way to go.

Replacing with a different-sized radiator is a lot trickier and not recommended if haven’t done any plumbing before.

Feel free to ask me any questions in the comment section below and I’ll do my best to help.

Please share this post if you find it helpful.

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