DIY – How to Fix Two Common Radiator Problems

Let’s look at how to resolve two common central heating problems – radiators that don’t get hot at the top and radiators which are cold in the middle and bottom.

Problem 1) Radiator cold at the top

When a radiator gets hot at the bottom, but doesn’t heat up at the top, this is almost always a sign that there is air in it. Hot water heats your radiators, but trapped air occupies space at the top of a radiator which is why this segment is not warming up. The solution to this is simply to bleed the radiator in question.

The first thing to do is to accurately assess the situation. Switch on your central heating, allow the radiators to warm up and then see which ones are suffering in this way. (An obvious point, but make sure they are all switched on when you do this.)

Before bleeding a radiator, switch the heating off and allow it to cool. The bleeding process often results in a bit of water escaping and you don’t want it to be scalding hot. Once the system is cool, you will almost certainly need a radiator key, although some radiators are bled with a conventional screwdriver, depending on the design. You should probably also use a rag or bit of cloth for any water which escapes.

At the top of the radiator, at one end or the other, there will be a valve. Open this with your radiator key or screwdriver. You will know it’s open by the hiss. Note that you don’t need to open it fully – just enough that the air is escaping. In fact, if you open it too much, it will take longer to close and more water will come out. You want to be able to react quickly. When water starts to appear (usually a dribble, but it depends on your radiator and how much you’ve opened the valve) it is time to close the valve as there is no more air to be released.

With many heating systems, you will then need to top up the pressure. Check the gauge on your boiler, which will normally indicate the correct zone and then use the filling loop to increase the pressure if necessary. There will be a lever or tap for the purpose, but consult your boiler’s user guide for instructions as to how to use it.

Problem 2) Radiator cold in the middle at the bottom

When this happens, it is usually a sign of ‘radiator sludge’. This not-so-technical-sounding term refers to an accumulation of rust and general dirt inside your system. Because of the way water flows inside a radiator, it will tend to build up at the bottom of the radiator in the middle.

There are two ways of removing it. The best way is to have the entire system professionally flushed, but you can also remove the radiator yourself to clear it out. This is a viable option if it seems like there’s only really one radiator that’s suffering from the problem. Before you start, be warned that this can be a messy job, so put down old sheets and towels and maybe get a bucket ready as well.

First, turn off the valves to isolate the radiator. Turn the thermostatic radiator valve off first and then the lockshield valve, which is typically the one under a plastic cover. You will need to use an adjustable wrench for the latter, turning it clockwise, but make a note of how much it has turned as you will need to reset it to the same place when you put the radiator back on.

After that, using two adjustable wrenches, loosen the thermostatic valve and you can then open the bleed valve with your radiator key (or screwdriver, depending on the radiator). Make sure you have a bowl or bucket positioned below the now-undone thermostatic valve because opening the bleed valve breaks the vacuum and causes the water (and much of the sludge) in the radiator to start flowing out.

Repeat the process with the lockshield valve and then tilt the radiator to remove excess water. After closing the bleed valve, you can then remove the radiator from the wall and take it outside where you can flush it through using a hosepipe. Having done this, you can reattach the radiator by doing the reverse of the above steps.

Aelheating specialise in radiators and provide solutions to everyday problems that occur with radiators. Aelheatings designer radiators brighten up households and are affordable accessory for any household.