One radiator not working: 5 common causes & how to fix

One radiator not working is usually the result of poor water flow. Typical causes are seized valves, blockages, an imbalanced system, or the presence of air. In this article, we’ll explain what you can do to fix this problem.

How to fix one radiator not working

The first thing to do is to check that the lockshield is open. This is a valve on the side of the radiator with a small plastic cap. It controls the maximum amount of water which can flow through the radiator. Don’t confuse it with the thermostatic valve or TRV, which is bigger and has numbers or temperature settings on it.

To check that the lockshield is open, turn the TRV on the other side of the radiator to its highest setting. Then, remove the lockshield’s plastic cap and use a pair of pliers to turn the spindle of the valve anti-clockwise until you can’t turn it anymore.

Next, feel the pipes which connect to the radiator. If one of them is hot, you know for sure that hot water is flowing to the radiator, but isn’t flowing through it properly.

If a radiator is cold at the top but hot everywhere else

This is due to air in the radiator, which takes up space where hot water should be. You can quickly fix this problem yourself by letting the air out with a radiator key. Check out our simple how-to guide on this topic: Bleed the radiators: how to bleed a radiator in 5 easy steps

If the radiator is cold at the bottom

This is most likely due to the presence of sludge in the radiator, a black, mud-like substance. It’s the result of a chemical reaction between the oxygen in the water and the steel of the radiators. It settles at the bottom of the radiator, restricting the flow of water before eventually obstructing it completely.

The most effective way to get rid of it is to remove the radiator from the wall and flush the sludge out with a hose. This may solve the problem without having to buy a new radiator. It may also be a good idea to have the system power flushed. Even if the sludge is only affecting one radiator, it could also affect others in the future and make your whole heating system less efficient. It could also damage the boiler. For more information on this topic, see our in-depth guide: Power flush: what is it, why do I need it & how much is it?

One radiator not working – the TRV

It’s easy to check whether or not the TRV has jammed. Remove the valve head and use the side of a spanner or radiator bleed key to press the pin down. The pin is spring-loaded and should pop back up again. If you can’t push it down then it has jammed. You may be able to use a pair of pliers to gently wiggle it and free it from what’s causing it to stick. Don’t yank it out as hard as you can, as you may either pull it out so far that you can no longer put the valve head back on, or pull it out completely and cause a leak. A gentle tap or two with a blunt object may also free it. Bashing it hard may also cause a leak and may also damage the valve further.

If you’ve managed to free the pin, you can check the mechanism by pushing it down again. However, if it gets stuck once more, it’ll probably get stuck again when you put the valve cap back on. In this case, replacing the whole valve is likely to be the best solution.

Imbalanced radiators

Another cause for one radiator not working properly is due to an imbalanced system. This basically means that water isn’t flowing through the radiators evenly. Water will always take the easiest route possible back to the boiler. By using the lockshield to control how much water can flow through each radiator, you can make sure that all of the radiators in your home heat up evenly. This is known as balancing the radiators.

If you notice that the one radiator not working is one of the furthest radiators from the boiler, balancing the heating system may solve the problem. This is also the case if two or three radiators aren’t getting hot.