Last updated on October 20th, 2023
A radiator not working, leaking, rusting, or 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.
In this post I’ll show you how to change a radiator based on my on-the-job experiences.
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.
- Undo the nuts on the valves with an adjustable spanner
- Disconnect the radiator valves if you are replacing them
- 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:
- Put some old towels under the radiator valves
- Close both valves fully
- Put a plumb tub under a radiator valve
- Crack the nut in between the valve and the radiator
- Let the water out slowly into the plumb tub
- Keep emptying the plumb tub until the water stops coming out
- Undo the nuts on both valves fully
- Lift the radiator off the wall brackets
- Take the old tails out of the old radiator and fit them on the new one with at least 15 wraps of PTFE tape
- Hang the new radiator on the old wall brackets
- Connect the tail nuts to the old valves and tighten them up with an adjustable spanner
- Fit the new bleed valve and blank nut that come with the new radiator
- Open both valves
- Bleed the radiator with a radiator bleed key from the radiator bleed valve
- Repressurise the boiler
- 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 definitely 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 one 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 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 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 and 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.
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:
- Lift the radiator onto the brackets
- Mark the long tails where they will sit inside the old valves with a marker
- Lift it off the brackets
- Cut down the tails using a 15 mm pipe slice (or a hacksaw will do the job)
- Rehang the radiator onto the brackets
- Fit new 15 mm nuts and olives on the tails
- Fit the radiator valves onto the tails and tighten the nuts up with a spanner
- Fit the bleed valve and blanking cap on the opposite side and tighten with a spanner
- open both valves,
- Bleed the radiator and repressurise the boiler
- Check all the other radiators for air with the radiator bleed key
- Repressurise the boiler again if needed and bleed all the radiators
- 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.
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 definitely 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.
How to Change a Radiator FAQs
How long does it take to change a radiator?
How long it takes to change a radiator depends on what needs to be done. In my experience, it takes anywhere from 20 minutes to 3 hours or more to change a radiator.
A 20-minute radiator replacement might be if you are changing a radiator like for like and keeping the same brackets, and you come across no problems at all.
A 3-hour or more replacement job might be replacing it with a different radiator, where you need to pull the floor up and adapt the pipes to fit the new radiator and measure and fit new wall brackets.
How easy is it to change a radiator?
It is not easy to change a radiator. If you are good at DIY, then changing a radiator might be easy when changing with the exact same radiator and using the old wall brackets.
Most of the time it’s not possible to find the exact same radiator to change as the old one is not made anymore, so you will most likely have to fit new wall brackets (difficult) and possibly adapt the pipes (difficult).
Is it possible to replace a radiator without draining the system?
Yes, it is definitely possible to replace a radiator without draining the central heating system. I have done it many times.
You have to close both radiator valves and isolate the radiator to do this, but if any of the valves are broken and won’t close (not uncommon), then you will have to drain the system.