You turn on your heating, and one or more radiators in your home stays cold. This is a common issue, and while it can be frustrating, the good news is that most causes of cold radiators can be resolved quickly, either on your own or with the help of a heating engineer.
Trapped Air
One of the most common reasons for a cold radiator is trapped air. Air builds up inside the radiator, preventing hot water from circulating properly. When this happens, the radiator feels cold at the top but warm at the bottom.
If trapped air is the problem, you can often fix it by bleeding the radiator. This releases the air that’s stuck inside, allowing hot water to flow freely again.
Turn off the heating and let the system cool down. Then use a radiator key to turn the bleed valve at the top of the radiator just enough so you hear a hissing sound as the air escapes. Once water starts to drip out, close the valve.
Turn your heating back on and check if the radiator is now warm throughout.
Radiator Valves Are Closed
Sometimes, it’s a really simple solution. If your radiator isn’t heating up, check the valves on either side. These valves control the flow of hot water into the radiator. If one or both valves are closed or only partially open, the radiator won’t heat properly.
Make sure both the manual control valve (on one side) and the lockshield valve (on the other side) are fully open. If either valve is closed, open it to allow hot water to circulate through the radiator.
Sludge Build-Up
Over time, dirt, rust, and debris build up inside your radiators, especially in older heating systems. This creates a sludge that settles at the bottom of the radiator, preventing water from circulating efficiently. If your radiator is cold at the bottom but warm at the top, sludge build-up is probably the cause.
If this happens you’ll need to flush the radiator to remove the debris.
First, turn off the heating and isolate the radiator by closing both valves. A lot of water comes out of radiators so place a deep enough tray underneath to catch any water, then use a wrench to loosen the nuts connecting the radiator to the valves.
Remove the radiator from the wall and take it outside to flush with water until it runs clear. Then reinstall the radiator, reopen the valves, and check if it heats up.
If the issue affects a few of your radiators, your best bet is to call a professional for a power flush, which cleans the entire system. A quick Google search for heating engineers near me will give you a list.
Faulty Thermostatic Radiator Valve (TRV)
The thermostatic radiator valve (TRV) is responsible for regulating the temperature of the radiator by controlling how much hot water flows through. The TRV often has a number from 1-5 and if the TRV is faulty or stuck, the radiator may not heat up as it should, leaving you with cold rooms.
A faulty TRV can block the flow of hot water, leaving the radiator cold. If you’re comfortable with certain plumbing jobs you can replace the valve yourself, but if not call a heating engineer.
Unbalanced Heating System
In some cases, the issue may not be with the radiator itself but with the overall heating system. An unbalanced system can lead to radiators that are farthest from the boiler receiving less hot water, causing them to remain cold while others in the house heat up properly.
To fix this, you’ll need to balance the system by adjusting the lockshield valve on each radiator. This involves reducing the flow to radiators that are heating up quickly, ensuring a more even distribution of hot water across the system. Balancing the system can be tricky, especially in larger homes with multiple radiators, so a heating engineer can ensure your entire system is set up properly.
When to Call a Heating Engineer
While many radiator issues can be fixed with basic DIY tasks like bleeding or adjusting valves, some problems require professional help. If you’ve tried the above fixes and your radiator is still cold, or if you notice persistent cold spots, unusual noises, or issues with multiple radiators, it’s time to call in a heating engineer.
If the problem is with the boiler, or there is significant water escape, you’ll need to call an emergency heating engineer.
Final
Whether it’s trapped air, a closed valve, or sludge build-up, it’s usually straightforward to restore warmth. If DIY solutions don’t work, or if you encounter more complex problems, contact a professional heating engineer. Regular maintenance can keep your heating system in good shape, ensuring a warm and comfortable home throughout the winter.
