One Radiator Not Working? Full Guide on How To Fix It

Author: Stuart Hunt - Published: 03.09.20
One Radiator Not Working

Do you have only one radiator not working on your heating system, therefore, the radiator is not heating up. If so, this is how to fix this.

First off, you should never start by just feeling the radiator as we need to identify whether the heat is not going to the radiator or if the radiator is just not heating.

The best way to do this is to check the pipework so too if they are getting hot, you will have two pipes going to your radiator one is the flow, and the other one is the return.

How To Fix One Radiator Not Working

  1. Remove air from the radiator that is not heating up
  2. Open the radiator valve fully on the radiator that is not heating up
  3. Remove the radiator from the wall
  4. Flush the radiator through with cold water
  5. Run water out of the radiator valve into a bucket
  6. Refit the radiator
  7. Balance heating system

How Much Would A Plumber Charge To Fix A Radiator That Is Not Working

An experienced plumber would charge on average between £90 and £130 to fix one radiator that is not working, with some companies charging as much as £65 per half hour.

The price to fix one radiator not working can vary depending on where you live in the UK with London being the most expensive with a cost between £100 and £160 and even up to £75 per half hour.

As an experienced plumber for over 20 years, I will guide you through the five simple steps to get that one radiator working again.

Air can be a common reason why a radiator gets cold; however, if you have air in a radiator, you will find that the radiator will only be cold on the top half of the radiator.

How To Remove Air From A Radiator

To remove air from a radiator, you will need to bleed the radiator from the bleed vent, to do this you would need a radiator bleed key.

On some more modern radiators, the bleed vent will have a slot for a flathead screwdriver.

To remove air from a radiator, you will need to bleed the radiator, turn the key or flathead screwdriver until you hear air escaping from the radiator.

Be careful not to turn the key or screwdriver too far as don’t want the bleed vent to come out of the radiator. If you don’t hear the air coming out of the radiator, don’t worry the vent may be blocked or painted over, at this point you will need to try to clear the vent with a pin and then try to bleed the radiator again.

Is Your Pipework Hot Or Cold?

If your pipework to the radiator that is not working is hot, then we know the heating is working, and the heat is flowing to that one radiator; therefore, we will now need to check if the valves are working.

Open The Radiator Valve Fully On The Radiator That Is Not Heating Up

You will need to make sure that both radiator valves are fully open if you have a TRV (thermostatic radiator valve), then don’t worry I will guide you through how to check this valve is working in a minute

To open the lock shed valve, you will need to remove the plastic headcover and use a spanner slow turn the spindle anticlockwise until fully open.

Never force your spindle, or you could break the spindle head which will mean you will need to replace the radiator valve.

If your radiator starts to get hot then great, if not don’t worry I have more ways to get that one radiator not working fixed.

How To Check If The TRV Is Working

If that one radiator is still not working then we now need to check the TRV, you will need to turn the TRV to the highest number in most cases that will be number FIVE, then start to unscrew the retaining nut which is holding on the TRV head on to the radiator valve body.

Under the TRV head, there will be a pin in the middle is the pin still down or up?


You can check this by pushing the pin up and down, if the pin is stuck down then using some long-nosed pliers to pull the pin upwards.

Once the pin is up then try to push the pin back down again, if the pin doesn’t pop back up you will need to change the TRV valve however if the pin does pop back the TRV is working fine.

If you need to change a TRV, then check out my guide on how to change a thermostatic radiator valve.

Is your radiator still cold?

If you have tried all of the above tips on How To Fix One Radiator not working and they have not worked then you will need to undo the radiator and remove the radiator from the wall.

Remove The Radiator From The Wall

At this point, you have tried all of the above methods to get one radiator that is not heating up working.

So now we will need to remove the radiator from the wall this can be good for two reasons.

  • Flush out the radiator with cold water
  • Flush out the pipework to that radiator

So how to remove a radiator from the wall - First thing to do is you will need to turn off both radiator valves using a small spanner and turn the spindle heads clockwise until they stop.

Never overtighten the spindles on the radiator valve as this could cause damage to the valve head and body which will result in having to change the radiator valves.

You do not need to turn off your water as you have turned off the isolation points which are the radiator valves, you also don’t need to turn off your boiler.

You will need to get a small pot to put under the radiator valve so that when you undo the radiator valve nut, you can catch the water.

If you are ready, you will need to grip the top of the radiator valve and then using an adjustable spanner undo the radiator back nut from the radiator slowly, making sure to catch to water in a pot until the water stops coming out of the radiator.

Now you can lift the radiator from the wall making sure you cover both ends of the radiator with your finger or thumb to stop any residual water left in the radiator from coming out and dripping onto the floor or carpets.

Flush The Radiator Through With Cold Water

Once the radiator is outside in the garden turned the radiator upside down so that the water inlets are at the top.

Now run a garden hose through into the radiator, so it starts to fill up and then overflows out of the radiator do this until the water begins to come out clean.

Tip the radiator back up the right way so that the bleed vent is at the top then run a garden through the radiator again to remove the last of the black sludge

Before re-installing the radiator back onto the wall, we can flush out the radiator valves and pipework to that radiator we have removed.

Run Water Out Of The Radiator Valve Into A Bucket

The best way to run water through the heating system is to turn on the heating, using a small bucket under the radiator valve and turn on each radiator valve one at a time to allow the water to flow into a bucket.

Top tip – if you have a washing machine hose, cut off one side of the hose where the screw thread is and then screw the other side onto the radiator valve this allows more control over the water coming out of the valve

Then repeat the process for each radiator valve.

You only want to let the water run out of the radiator valve until the water coming out is hot; however, be careful not to burn yourself while carrying out this part of the process.

If you have a combination boiler, make sure you have pressure in your boiler before doing this, also make sure you do not drain all the water from your heating system.

Refitting The Radiator

Now you have hot water going to the radiator you can refit the old radiator back onto the wall.

Place the radiator onto the wall brackets, using adjustable grips to hold the top of the radiator valve then using a spanner tighten up both back nut onto the radiator.

Turn on the radiator valve one at a time until they are fully open hot water should now start to run into the radiator.

Bleed the radiator to remove all the air, and the hot water goes to the top of the radiator.

If you find the radiator starts to cool off, you might need to balance the heating system.

Re-Pressurise A Combination Boiler

If you have a combi boiler, you will need to re-pressurise your boiler.

All combi boilers will have a pressure gauge which should be set to a maximum pressure of 1.5 bar a red arrow typically indicates this also there should be a green section within the gauge which also shows the correct pressure.

To re-pressurise your boiler you are best to read your boiler manufactures instructions as they all can be different, I wouldn’t want to give you false information because your boiler may be different to the next person.

Balance Heating System

To balance a heating system, you will need to reduce the flow out of the other radiators on the system you can do this by going to the other radiators and reducing the flow on the lock-shield side of the radiators

The lock shield side of the radiator is the side of the radiator where you have not got a TRV or a head that will turn off the radiator. The lock shield will just have a plain cover that will just keep turning, and therefore you will require a spanner to turn this side off.

Using a spanner close all the lock-shield valves a bit to balance the heat so that all the radiators are the same or similar temperature - for a full guide on how to balance a heating system click here.

Now you have your heating running and followed my guide on how to fix one radiator not working your radiator should now be heating up

I hope so.

There may be a small chance that the one radiator has not started to heat up after following this guide and you have carried out all of the basics.

If that is the case, I would advise you to contact a plumber as there may be something larger wrong with the heating system that the basics would not be able to fix.

A plumber will be required to trace the source of the problem so that they can fix the problem you can get the radiator working again.

For tips and a guide on how to change a TRV radiator valves I have a guide for you here

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