Why are my radiators cold at the bottom?
Why are my radiators cold at the bottom?
One of the common problems with radiators, particularly old ones, is when they’re hot at the top but cold at the bottom. If one of your radiators is only hot in the top half, it won’t heat your room up as well as it should. This could leave you getting cold, or it might mean you end up turning up the thermostat to try and stay warm.
If you find any of your radiators are cold at the bottom, you shouldn’t turn up your thermostat to compensate. This will make your boiler work harder, but it won’t heat up the cold patch. Your energy bills might just go up without your room getting warmer. What you need to do is fix the problem so everything works properly.
In this article, we’ll explain why radiators get cold at the bottom and what you can do to fix it. Normally, when the bottom of a radiator is cold it’s because there’s a build up of sludge in it. We’ll explain the different ways of fixing this, and we’ll explain how you can stop it happening again. As well as that, we’ll explain some other things that might be causing the problem and how you can fix them.
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Why is my radiator cold at the bottom?
There is one main reason why radiators get cold at the bottom, and most people only need to worry about this.
The most likely reason why your radiator is cold at the bottom is there’s a build up of sludge inside it.
Radiators, pipes and other parts of our home heating systems are normally made of copper, iron and steel. As water flows through and around all these parts, compounds like magnetite and haematite are formed, and deposits like limescale build up. Eventually, these impurities build into a sludge that can settle in parts of our heating systems. The normal place for this to happen is in radiators.
When sludge forms at the bottom of a radiator, hot water flow is restricted to the area, and it doesn’t heat up properly. This can happen with just one radiator or with several of them.
Sometimes, radiators get cold at the bottom for other reasons. Other possible reasons for the bottom of a radiator being cold are:
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Faulty TRV valve
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Poorly balanced radiator system
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Malfunctioning pump
These problems are much less common, but they’re worth looking at if the culprit definitely isn’t sludge in the system. They might be reasons for new radiators being cold at the bottom, for example.
Sludge making the bottom of the radiator cold
The sludge that forms in radiator systems, is a thick and gritty substance. Once it starts to build up somewhere, it becomes easier for more to get stuck in the same place.
It’s a common problem in old radiators simply because they’ve had more time for sludge to build up. As well as this, radiator design can affect things:
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If you have cast iron and steel radiators, they can react more with the water and create more sludge in your system.
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Column radiators can trap sludge in the bottom of vertical sections.
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Decorative radiators can have intricate designs with narrow channels that trap sludge.
Aluminium radiators are an alternative to iron and steel that create less sludge. They also have other benefits like environmental friendliness and cost-effectiveness, they are becoming increasingly popular. If you’re looking for new central heating radiators, however, don’t be put off buying cast iron or steel radiators. You can use corrosion inhibitors to prevent sludge build up, and some modern radiators are designed to resist the problem.
Poor water flow making a radiator cool at the bottom
If sludge isn’t the culprit, you can check if the problem is caused by a poorly balanced radiator system, a poorly functioning pump or a faulty TRV valve. These problems can happen with any radiator system, including with new radiators that are cold at the bottom.
In each case, what could be happening is that the water flow is being restricted to the problematic radiator. With restricted water flow, it’s possible there isn’t enough water getting into the radiator to heat it up completely. In this case, the hot water could rise to the top and heat only the top part of the radiator.
How to fix radiators that are hot at the top but cold at the bottom
If you have a sludge build up in a radiator, you can fix the problem yourself by taking it off and flushing the sludge out with a hose. If this isn’t a good option, you can hire a competent and suitably qualified heating engineer to power flush your heating system or treat it with radiator cleaners.
You can also look at other fixes if sludge isn’t the problem.
Getting your radiators working properly again will warm up your house and make your entire heating system more efficient.
Be aware that bleeding air out won’t normally help if you have a radiator that’s hot at the top but cold at the bottom. Bleeding air out helps with radiators that are cold at the top or have cold patches.
Remove your radiator and manually flush it
If you have some DIY experience, you can remove a radiator with sludge in it and clean it out yourself.
Here are the steps in brief:
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Step 1: Turn off your heating system, and let the radiator cool down.
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Step 2: Isolate the radiator by closing the TRV valve on one side and the lockshield valve on the other. Take note of how many turns it takes to close the lockshield valve, and look at the settings on the TRV valve.
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Step 3: Next you need to drain all the water from the radiator. To do this, place a large tray under the swivel nut connecting the radiator to the inlet pipe next to the TRV valve. Undo the swivel nut and then release the bleed valve at the top of the radiator. The water will drain into the tray. Make sure you have spare trays if you need, and don’t spill any water. You’ll need to be able to catch all the water stored in the radiator.
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Step 4: Remove the radiator by undoing the other swivel nut on the outlet pipe on the other side and disconnecting from the mount that holds it to the wall.
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Step 5: Take the radiator outside and blast water through it with your hose to clear the sludge. Make sure you clear it from both sides and you do a thorough job. Hold the hose tightly into the inlet and outlets with the hose on high pressure. Tapping it with a rubber mallet might help.
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Step 6: Reconnect your radiator. Reattach your radiator to its wall mounts and to the inlet and outlet pipes. Then close the bleed valve. After this, reopen the TRV valve and lockshield valve to the same point they were at before.
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Step 7: The last step is to bleed your radiator so it heats up evenly, you may need to bleed other radiators in the home due to the air added to the system.
Chemically flush your heating system
Another way to fix radiators that are hot at the top but cold at the bottom is with a chemical flush. This is a good choice if you have lots of problematic radiators or if you don’t want to take a radiator off the wall. Doing a chemical flush involves draining and refilling your entire heating system, and it also means working with chemicals. You should leave the job to a competent and suitably qualified central heating engineer.
Central heating cleaners do a great job of breaking down sludge and limescale. You can also add a central heating inhibitor and protector to prevent sludge from building up again.
It’s best to chemically flush an old system before you add an inhibitor to prevent sludge build up. With new heating systems, this isn’t necessary.
Power flush your heating system
You can also go a step further than chemical cleaning by hiring a central heating engineer to power flush your heating system.
In a power flush, a central heating engineer will flush water and chemical cleaners through your system under pressure, using a specially designed machine. This is a more powerful cleaning process, but it takes longer and requires much more care. Usually, this is best when there’s a heavy sludge build up or in large heating systems.
If you think power flushing might be a good idea, speak to a competent and suitably qualified heating system engineer.
Other fixes
If sludge isn’t the problem, then the next thing is to see if poor water flow is the reason. This is common when new radiators are cold at the bottom, but it can happen in any heating system. Some common causes of this are:
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Faulty TRV valve
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Poorly balanced radiator system
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Malfunctioning pump
You can often check if a TRV valve works by testing the TRV pin. To do this, you take the top part off and press the pin to see if it moves freely up and down. You need your TRV to work correctly to maintain consistent water flow to your radiator and consistent temperatures in your room.
You won’t be able to fix a malfunctioning pump yourself. This is a job for a professional. If a poorly balanced system could be the reason, you need to be able to diagnose the problem and rebalance your radiators.
How to prevent your radiator getting cold at the bottom
Once you’ve cleared sludge out of your radiators, you’ll want to stop it forming and causing a problem again. It’s also a good idea to carry out some preventative measures when you are fitting new radiators.
The main ways to stop sludge forming are with a central heating inhibitor or a magnetic filter.
Central heating inhibitor
Central heating inhibitors work by adding a protective coating to stop iron and steel in heating systems from rusting and reacting with water to form the compounds that help to make sludge. They also break down particles in the water, prevent scale formation and lubricate moving parts in your heating system.
Magnetic filter
Magnetic filters, also known as magna cleaners, work by attracting the metallic elements in sludge into a filter that removes them from the water. Some also use a mechanical filter to take out non-metallic particles as well.
As well as using inhibitors and filters, it’s also a good idea to remember to have your central heating system regularly checked and maintained by a professional. This is particularly important in old systems where sludge is more likely to be a problem.
If you’ve got a smart heating system, make sure you keep it free from sludge so you get peak performance.
Radiator is cold at the bottom key takeaways
If one of your radiators is hot at the top but cold at the bottom, it will make the room colder and it could affect the efficiency of your heating system.
While it’s not an easy problem to fix, it is something you can fix by yourself if you have some DIY experience and you’re prepared to get your hands dirty. Otherwise, you can call a competent and suitably qualified central heating engineer to do the job for you.
Remember to look at central heating inhibitors for preventing sludge build up in the first place.
Find out everything you need to know about buying new radiators.