Why radiators get cold at the top?

Have you ever wondered why the top of your radiator feels icy while the bottom is piping hot? The culprit behind this common conundrum is often trapped air, and we’re here to guide you through the simple fix built right into your radiator design.

The science behind this issue is quite straightforward. Air is significantly less dense than water, about 900 times lighter, to be exact. This density difference means that, even under slight pressure, air tends to rise and accumulate at the highest points within your radiator. Once these pesky bubbles find their way in, they become stuck at the radiator’s peak, leaving you with a cold top and an ever-increasing volume of trapped air.

Water acts as an effective barrier against air, which is why you can submerge an upside-down cup into a bath without it getting wet on the inside. Once the air ascends, it essentially becomes trapped, unable to escape the system. Furthermore, air is not as efficient at conducting heat as water, and the air in the top half of your radiator remains unheated, exacerbating the chill.

So, how can you bring back the warmth to your radiator? The good news is that trapped air is a common issue, and radiators are equipped with a solution built right in.

At the top of your radiator, you’ll typically find a bleed valve. These valves come in various forms, so you’ll need to identify the one on your radiator. Sometimes it’s situated at the radiator’s end, pointing along the wall, while in other cases, it’s a small bolt located at the rear. Heated towel rails may have the valve at the top, pointing upward. Most bleed valves require a bleed key, although some can be opened with a screwdriver or spanner.

Here’s how to tackle the problem:

1. Ensure your heating is turned off and has cooled for about half an hour. The water inside can be scalding, and it’s essential to work safely.
2. Place rags or towels on the floor under the valve to catch any potential water drips. Position a container like a cup or tub directly beneath the valve. If your radiator is against a wall with wallpaper, consider protecting it with card or plastic sheeting.
3. Gently turn the valve clockwise until you hear hissing. This sound indicates that the trapped air is escaping, which is precisely what you want. If the cold portion extends halfway down the radiator, you can open the valve a bit more to expedite the process. However, be cautious not to remove it completely, as working with flowing water can be tricky. For radiators with only a few inches of cold space, keep the valve slightly open, as it will empty rapidly.
4. Now, patience is key. As you release the pressurized air, the radiator will fill with water silently. Since the heating system is turned off, you won’t immediately feel the difference in temperature. However, be vigilant and ready to close the valve as soon as you see water emerging. The bleed hole is tiny, so only a small amount of water should escape. Still, it’s a good idea to take precautions to protect walls and carpets.
5. Close the valve gently; it doesn’t require excessive force. Over-tightening could lead to threading issues with the bolt, creating a bigger problem.

With trapped air successfully released, your radiator should regain its warmth and efficiency. This simple procedure is one solution that can make a world of difference in keeping your living spaces cozy during the cold months but the other option is to give Capital Plumbing a call and have it done by a professional.