Why are my radiators getting cold at the bottom

Winter has arrived! And it’s that time of the year when you highly rely on your boiler and radiators to provide your homes with heating and hot water to keep your family warm. But a common issue many people in the UK face is the radiator getting cold at the bottom and warm at the top. When radiators become cold at the bottom, it usually means that sludge buildup has blocked the hot water’s flow or is restricting it.

This is not a significant problem, but if not properly investigated and solved, it can become a matter of concern, as your home will not be adequately heated and there will be inconsistent distribution.

Is your radiator also getting cold at the bottom? Don’t worry, as it does not mean that your boiler is faulty. It means your radiator needs a little attention.

In this blog, I will be telling you what you can do to remove the cold patch from your radiator, along with the possible measures that you can take to prevent the problem. Before we get into how to remove cold spots from the radiator, it is vital that you first understand how a radiator works.

How does a radiator work?

Radiators work through a simple heat transfer process known as convection. It is connected to your boiler (central heating system) via pipes. When you turn on your boiler, it heats the water and transfers it to your radiator. From there, the hot water is heated by the surrounding air via convection to heat your home. After the heated water has completely flown through your radiators, it travels back to your boiler to get heated again.

It is essential to understand that water does not stay in your radiators all the time and only stays to heat your home or a particular room. Once the heated water has properly warmed the room, it flows from one radiator to another. After completing the flow around your radiators, it flows back to your boiler in a colder state, where it is heated yet again. This back-and-forth process makes the radiator prone to airlocks and cold spots.

What are the reasons and causes of radiators getting cold at the bottom and hot at the top?

Reason

The radiator getting cold from the bottom indicates that the flow of hot water is being restricted due to blockages. The common reason behind this blockage is a buildup of sludge.

Cause

As mentioned above, the heated water from your boiler continuously flows through your radiators. The radiators are made up of steel, and with passing time, the continuous flow of water forms iron oxides (hematite and magnetite) that build up over time and prove to be a significant cause of blockage.

Additionally, other minerals accumulate in the water, causing impurities like limescale to accumulate. These impurities cause sludge buildup that blocks the water flow from the bottom, making it cold.

Suppose you are experiencing inconsistent heating flow around your home. In that case, it is more likely that a lot of sludge has built up at the bottom and needs to be removed. Remember that sludge buildup will not be removed by itself, as the pressure at which water is flowing through the radiators must be increased.

Also, the buildup of sludge will not be cleared by bleeding out the radiators, as bleeding is only good for removing cold spots from your radiators.

How do we fix radiators that are getting cold from the bottom?

Radiators getting cold from the bottom and warm at the top is a problem that, left unattended, can cause problems for your boiler operation. You must take the necessary steps to solve the problem. Suppose only one of the radiators in your home is getting cold from the bottom. In that case, you can fix the problem by manually flushing your radiator.

Suppose more than one radiator is getting cold from the bottom. In that case, you might chemically or power flush your radiators; therefore, you should get in touch with a professional because you cannot do this process yourself. Let’s discuss both methods in detail:

How to manually flush your radiators

Suppose only one of your radiators is getting cold from the bottom. In that case, you can solve the problem by manually flushing your radiator without needing assistance from a gas-safe engineer, considering you are good at performing DIY solutions.

Now, let’s move on to the step-by-step procedure:

Step 1:

The first step is to isolate your radiator, for which you must turn down your thermostatic radiator valve to zero (if you have one). Then, locate the lock shield valve on the opposite side of the radiator, which will be covered with a cap. Remove the cap and, with the help of pliers or a spanner, turn it a quarter and a half to turn it off.

For more details, read How to Isolate a Radiator.

Step 2:

The next step is to prepare for water spillage, as you must bleed your valves. To prevent the mess, you will need a piece of old cloth or a towel to lay down beneath the connector nuts. Also, place a plastic bowl over the towel to catch the water and prevent it from spilling on the floor.

Step 3:

Now, with the help of a plier or a spanner, loosen up the radiator nuts slightly and let the gunky black water drip out that is built due to excessive corrosion and lack of maintenance.

Step 4:

The next step involves opening the bleed valve at the top of your radiator. For that, you will need a bleeding key. But before opening the valve, place a bowl near the valve to catch the water. Then attach the key to the bleeding screw, let the air escape, and wait for the hissing sound.

After the hissing sound ends, the water will drain out and fill the bowl. It is advised to have another bowl in place just in case there is too much water trapped inside.

For more details, read How to Bleed a Radiator.

Step 5:

Now, after the water is fully drained, undo the valves, remove the radiator from its brackets, and take it outside to begin the flushing process and remove the sludge.

Step 6:

Place the radiator in your garden and take a garden hose pipe, attach one end to the tap and the other to the inlet valve, and turn on the tap. Continue flushing the radiator until the dirty water stops coming on the other side. For extra satisfaction, attach the hose to both radiator openings until the clean water flows out.

Step 7:

After thoroughly flushing your radiator, please bring it back inside and reattach it to your brackets. Reattach the pipes and valves. The water will start flowing into your radiator, so stay ready with the bleed valve to tighten it as soon as you see the water escaping.

Step 8:

Now, it is time to test your system. After completely reattaching your radiator, it’s time to test the system by turning back on your heating system. Wait for 15-20 minutes, allow the system to heat up, and then touch it from the bottom, and you will notice that it is evenly hot at the bottom.

Remember, if you have a conventional feed and expansion system, i.e., a heat-only boiler, your system will repressurize itself. On the other hand, if you have a pressurised system like a combi-boiler, you will need to repressurize it with the help of a filling loop.

What should I do if more than one radiator is affected?

When you don’t use your radiators more often or don’t maintain them annually, the buildup of sludge becomes severe and affects multiple radiators in your home. For that, you will require the assistance of a certified professional who will perform a chemical or power flush to remove the sludge altogether.

What is a powerflush?

Power flushing your radiators is a process to remove the buildup of sludge, rust, debris, and other impurities from your radiators and pipes. The process involves a powerful pump being connected to the pump head, circulation pump, and tail of the radiator. After that, water is circulated at high pressure along with the cleaning agents to remove impurities from your system.

After removing the impurities, the professional will use clean water to drive out the contaminated liquid and ultimately dispose of it after removing sludge and other contaminants from it.

What is chemical flushing?

A chemical flush is the process of removing sludge, rust, and debris from your radiator to allow the water to flow more smoothly. Contrary to a power flush, a chemical colour involves using gravity. It releases chemicals that dissolve the sludge and, with the help of a manual water flush, removes the contamination from your system.

How do I prevent my radiators from getting cold in the future?

After successfully getting sludge and debris removed from your system, you must take the following measures to prevent radiators from getting cold at the bottom in the future:

• Regularly clean your radiators.

• Use a scale reducer and add it to your water to reduce limescale, which makes sludge buildup more severe.

• Add a central heating inhibitor to your water, forming a coated layer to prevent the buildup of limescale and sludge and keep the water running smoothly.

• Get magnetic filters installed, as they are crucial in attracting sludge and other metallic debris before they accumulate in your radiators and interrupt the heating flow.

Conclusion

So here you have it. After reading the above blog, cold radiators from the bottom shouldn’t be a concern. However, if you have any other issues related to your radiator, such as how to bleed a radiator, how to isolate a radiator, how to measure a radiator, and more, then visit our blogs section and enter your query in the search box to find the related articles. If you don’t see the necessary guide in our blogs, please contact us at 0345 3192 247, and one of our representatives on call will assist you with your problems.

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