Boiler Works But Radiators Stay Cold in the UK

Boiler Works But Radiators Stay Cold in the UK
A boiler that is functioning properly is essential for keeping your home warm and comfortable during the colder months in the UK. However, if your radiators stay cold even when the boiler is on, it can be frustrating. In this article, we'll explore some of the possible reasons why your radiators might be staying cold despite your boiler working correctly.

Blocked Pipes or Radiators

One of the most common reasons why radiators stay cold even when the boiler is working is due to blocked pipes or radiators. Over time, pipes and radiators can accumulate rust, sludge, or other debris that can hinder the flow of water through the system. If this happens, your boiler may be working correctly, but the water won't be able to reach your radiators, resulting in cold rooms.

To fix this issue, you'll need to have a professional power flush the system, which involves flushing water and cleaning agents through the pipes and radiators to remove any debris. This process can be costly, but it's essential to keep your heating system functioning correctly.

Call a heating engineer

Air in the System

Another common cause of cold radiators is air in the system. Air can get trapped in your radiators, preventing hot water from flowing through them and heating up your rooms. You may notice that some radiators are colder than others, which could be a sign of trapped air.

To fix this issue, you'll need to bleed your radiators, which involves releasing any trapped air. You can do this yourself with a radiator key or hire a professional to do it for you. Simply turn off your heating system and wait for the radiators to cool down. Then, locate the valve at the top of your radiator and use the key to release the trapped air. You'll hear a hissing sound as the air is released, and when water starts to come out, you'll know that the radiator is bled.

Faulty Thermostat

If your radiators are staying cold even when your boiler is working and the pipes and radiators are not blocked, the problem could be a faulty thermostat. A thermostat is a device that controls the temperature in your home by turning your heating system on and off. If your thermostat is not working correctly, it may not be sending the signal to your boiler to turn on, even if the temperature in your home is below the desired level.

To test your thermostat, turn it up to the highest setting and wait to see if your heating system turns on. If it doesn't, the thermostat may be faulty and need to be replaced.

Faulty Pump

Another reason why radiators can stay cold is due to a faulty pump. The pump is responsible for circulating the hot water from your boiler to your radiators. If the pump is not working correctly, the water may not be flowing through the system, resulting in cold radiators.

To check if your pump is working correctly, listen to it when your heating system is on. You should be able to hear a humming sound, which indicates that it's working correctly. If you don't hear anything, or the sound is weak, the pump may be faulty and need to be replaced.

Boiler Pressure

Finally, the pressure in your boiler could also be the cause of cold radiators. The pressure in your heating system should be between 1 and 1.5 bar. If the pressure is too low, your radiators may not be receiving enough hot water, resulting in cold rooms. You can check the pressure on your boiler by looking at the pressure gauge, which is usually located on the front of the boiler. If the pressure is too low, you'll need to repressurize the system by adding water. You can do this by using a filling loop, which is a hose that connects to the boiler. Make sure to follow the manufacturer's instructions when repressurising your boiler, as adding too much water can cause other issues.

Faulty Diverter Valve

A faulty diverter valve is another potential reason why your radiators might stay cold. A diverter valve is a component in your heating system that directs hot water to either your radiators or your hot water cylinder. If the diverter valve is faulty, it may not be directing hot water to your radiators, resulting in cold rooms.

To check if your diverter valve is working correctly, turn on your hot water tap and see if your radiators start to heat up. If they do, the diverter valve may be faulty and need to be replaced.

Boiler Faults

In some cases, the problem may lie with your boiler itself. There are several faults that can cause your radiators to stay cold, including a faulty pump, blocked heat exchanger, or a broken thermostat. If you've ruled out all other potential causes and your radiators are still cold, it's best to contact a professional heating engineer to diagnose and fix the issue.

Contact a boiler technician

Preventing Future Issues

To prevent future issues with cold radiators, it's important to maintain your heating system properly. This includes having it serviced annually by a qualified heating engineer, who will check for any potential issues and fix them before they become major problems. It's also essential to power flush your system every few years to remove any debris and ensure that water can flow freely through the pipes and radiators.

In addition, bleeding your radiators regularly can help prevent air from getting trapped in the system and causing cold spots. Make sure to check the pressure in your boiler regularly to ensure that your radiators are receiving enough hot water.


If your boiler is working correctly, but your radiators are staying cold, there could be several potential causes, including blocked pipes or radiators, air in the system, a faulty thermostat, faulty pump, low boiler pressure, faulty diverter valve, or boiler faults. By diagnosing and fixing the issue promptly, you can ensure that your home stays warm and comfortable during the colder months in the UK. Remember to maintain your heating system properly to prevent future issues and contact a qualified heating engineer if you're unsure how to fix the issue yourself.

With a boiler cover plan, avail the benefits of boiler and central heating coverage. This will serve you as a monthly or yearly insurance policy to cover your boiler.