Ideally, a radiator should have a uniform temperature when switched on. This is because they function to distribute heat evenly.
So, they will be hot to touch from top to bottom and right to left. This is due to heat loss from the warm water through the radiators.
Radiators must be relatively the same temperature throughout, rather than being cold to the touch at either the top or bottom.
However, if the top of your radiator is cold, there may be a deeper problem. Fortunately, you can easily fix it yourself.
How Do Radiators Work?
Radiators function to keep your room warm. To do so, they take the heat from heated water.
Hot water from the boiler enters the radiator and gets directed inside the radiator in a fixed direction. The water first moves sideways, then upwards, then downwards, and finally, to the exit.
As a result, the entire radiator has a flow of hot water. So, ideally, a radiator must have uniform heating throughout.
Water follows a double loop, so hot water enters the radiator via the flow loop. The cooled water that exits the radiator returns to the boiler for reheating via the return pipe.
An arrangement like this is most commonly found in heating systems. However, recent systems have different arrangements where the flow and return loop may not be connected and may work independently.
However, whichever the case, a radiator should have a uniform temperature throughout when turned on.
Check If Your Radiators Is Cold At The Top
First off, check if your heating is turned on. Also, if you have just switched on your heating system, it will take some time for the water to get heated and circulated.
Also, if you notice that the radiator is heating at the bottom and not at the top, it could mean that hot water has just started entering your radiator. As it enters via the flow pipe, which is generally located near the bottom, your radiator will first heat the bottom, and when the hot water rises, the top will get heated as well.
However, if your system has been running for at least 20 mins, and you still notice that the radiator is cold at the top, this indicates some issue with the radiator. To confirm, glide your hand across the top, middle, and bottom to detect a temperature change.
Why Do Radiators Get Cold At The Top
Trapped air is the most common reason behind cold radiator tops. As water is much denser than air, it settles at the bottom, and the air floats upwards.
Also, the trapped air bubbles circulate along with water. But when they reach a high point like radiator tops, they stay there. As more air bubbles reach the radiator, more air will get trapped.
As water is very efficient in conducting heat, it will get heated, while air does not conduct heat and won’t get heated up.
So, the radiator will have hot water at the bottom and cold air at the top. This is why radiators get cold at the top.
How To Fix Cold Radiator Top And Achieve Uniform Heating
Trapped air in radiators is a common problem, and you fix the problem by bleeding the radiator. It is a simple fix that even the most inexperienced DIYer can try.
Requirements:
- Bleed key
- Container (to catch spilling water)
- Paper towels or rag cloth
Steps To Bleed Your Radiator
- Turn off your central heating and ensure your towel rails and radiator have cooled down.
- Find the bleed valve (often located at the top of the radiator).
- Place rugs or towels to protect the area below the valve. Also, protect the surrounding walls and any area where water may squirt.
- Place a small container below the valve to catch spilling water.
- Insert the bleed key in the valve and turn clockwise. Keep turning until you hear hissing. The hissing sound is proof that the air is leaving the radiator.
- You can rotate the key further to speed up the process, but ensure it only comes out partially.
- As the air is exhausted, the hissing quietens.
- Close the valve as soon as you see water coming out.
As mentioned, you can open the bleed valve with a bleed key. However, you can open some bleed valves with a spanner or a screwdriver.
Bleed keys are easily available in hardware or DIY stores. However, if you cannot find one, try to open it with a screwdriver.
Also, the bleed valve is tiny, so you will not have much water spillage. But it is better to be prepared.
During the process, make sure you take two precautions:
- Make sure the system is cooled. Otherwise, scalding water in the radiator can bleed through the valve and cause burns.
- When closing the bleed valve, do not exert too much pressure. Close it gently; it does not have to be very tight. Overtightening can bolt the thread, which will become a bigger issue.
Preventing The Recurrence Of Cold Radiator Tops
Sometimes, air bubbles can get trapped in the system when it is getting filled. This is because water has some amount of trapped air. You can change the pressure and temperature to help release the trapped air.
As the system is almost always under pressure, it is virtually impossible for air to enter from outside. So, the air is generated due to some chemical reaction within the system.
This chemical reaction is corrosion. As the radiator and the pipes corrode, sludge and gas form. The sludge collects at the bottom of the radiators while the air bubbles float to the top.
It is a very slow process, and you will likely notice the issue only after a great deal of corrosion has taken place. So, to eliminate the gas issue, you will have to deal with the corrosion.
Fix: Add a retardant to the system. It eliminates corrosion or, at least, slows it down.
Other Common Radiator Problems
Like a cold radiator top, sometimes, the radiator can get cold at the bottom. Cold radiator bottoms are also a common issue. The accumulation of sludge at the bottom of the radiator bottoms causes it.
As sludge builds up, it restricts the flow of hot water to the bottom. This results in cold radiator bottoms. To fix the problem, you must remove the sludge. You can do this with manual flushing, a power flush, or a chemical flush.
You can do manual flushing yourself. However, you will have to bleed the radiators and remove them to clean the sludge manually.
Power flushing needs specialized equipment. It makes use of pressurized water to remove sludge.
Chemical flushing involves introducing a chemical agent into the system, which acts as a cleaning agent and eliminates sludge. It is similar to using a chemical cleaner for your drainage system. The agent helps dissolve the sludge, which can then be eliminated.
Conclusion
If you have a radiator that remains cool at the top but heats at the bottom, it is probably due to trapped air. As air rises to the top of the radiator, hot water is not circulated in the area, causing it to stay cold.
You can resolve the problem by simply bleeding the bleed valve. It will release the trapped air, and water will automatically gush into the empty space.