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Last updated: 22nd August, 2023


Radiators Not Heating Up: How to Fix?

Radiators Not Heating Up: How to Fix?

Key takeaways

  • Identify and resolve common radiator issues by understanding heating system components and their functions.
  • Effectively troubleshoot radiator problems through the recognition of common causes and applying the appropriate solutions.
  • Maintain optimal radiator performance by adopting preventative measures and seeking professional assistance when necessary.

Experiencing issues with your radiators not heating up can be attributed to various factors, from trapped air to malfunctioning components in the central heating system.

Radiators play a vital role in keeping our homes warm during the colder months, so it's essential to ensure they function efficiently. 

One common issue faced by homeowners is radiators failing to heat up properly, causing discomfort and an unwelcoming indoor environment. 

This UK guide aims to provide valuable information on how to identify and resolve common radiator problems, from the various components to troubleshooting tips and when to seek professional assistance.

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Understanding the underlying causes of radiator issues is crucial in addressing them effectively and preventing future problems. 

By examining common causes, learning how to identify which component is failing, and becoming familiar with heating system elements, individuals can efficiently troubleshoot issues and conduct appropriate maintenance or repairs. 

Additionally, having an awareness of preventative measures and potential considerations, homeowners can help ensure their radiators and heating systems remain in optimal working order.

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Understanding Radiator Problems

Cold Radiator

Cold radiators are a common issue in many households. If your radiator is not heating up, it could be due to various reasons. One possibility is that the radiator valve is turned off, preventing the flow of water. 

Another reason could be the presence of an airlock in the radiator or pipes, obstructing the circulation of hot water. Additionally, a buildup of sludge in the radiator can also cause it to remain cold. Regular maintenance and inspection of your radiators are essential to avoid these issues.

Air in the System.

Air can get trapped in the radiator system and create problems with heating. When air is present in the system, it tends to cause uneven heating, with the radiator having hot and cold patches. 

To fix this issue, locate the radiator bleed and use a radiator key to release the trapped air. Bleeding the radiators will improve water circulation and ensure even heat distribution across the system.

Radiator Valve Issues.

Radiator valve issues can also cause problems with the heating system. The thermostatic radiator valve (TRV) is responsible for regulating the temperature by controlling the flow of water into the radiator. If the valve becomes blocked or stuck, it may not function properly, resulting in poor heating. 

To check for valve issues, remove the thermostatic valve head and inspect the raised pin on the valve. If the pin is stuck or seized, gently push it down to free it, ensuring the smooth flow of water through the radiator.


Gurgling Noises

Gurgling noises in the radiator system might indicate the presence of air or trapped water within the pipes. These sounds occur when the water struggles to flow through the system due to air pockets or build-ups of debris. 

To resolve this issue, bleed the radiators to release trapped air and ensure that the pipes and radiators are free from blockages and obstructions.

It's important to address radiator problems promptly to maintain a warm and comfortable home environment. Understanding the root causes of these issues and implementing the appropriate solutions will help you keep your radiators functioning effectively.

Identifying Common Causes

In this section, we will explore some common causes for radiators not heating up, focusing on trapped air, debris and dirt, rust and sludge, and limescale. Understanding these issues can help homeowners identify the problem and take the necessary steps to fix it.

Trapped Air

One of the leading causes of a radiator not heating up is trapped air. This can occur when air accumulates inside the radiator, thereby impeding the flow of hot water. To address this issue, you can bleed the radiator by using a radiator key or a flat-head screwdriver to open the bleed valve. 

Be sure to place a cloth or container beneath the valve to catch any water that may leak out. Slowly open the valve, releasing the trapped air; you'll know when it's complete as water starts to trickle out. Don't forget to check the boiler pressure and top it up if necessary, as bleeding the radiator can sometimes cause a drop in pressure.

Debris and Dirt

Over time, debris and dirt can accumulate in your central heating system, causing blockages and impeding the flow of hot water to your radiators. 

A common solution for this issue is to flush the system, which can be done by a professional heating engineer. They will connect a high-pressure machine to the central heating circuit and use chemicals to break down and dislodge any build-up. 

Checking and cleaning the radiator valves can also improve the flow of hot water in the system.

Rust and Sludge

Corrosion within the radiator can lead to the formation of rust and sludge, which can obstruct the flow of water and reduce the radiator's heating efficiency. In severe cases, rust can even lead to leaks, causing further damage to the heating system. 

To tackle this problem, consider using a chemical inhibitor, which can help slow down corrosion and extend your radiator's lifespan. Alternatively, if the problem is extensive, you may need to replace the radiator entirely.


Limescale is a common issue in areas with hard water, resulting from a build-up of minerals within the heating system. This can lead to reduced heat output, increased energy consumption, and even damage to the central heating system components. 

To tackle limescale, you can add a limescale inhibitor to the system's water supply, or consider using a water softener device that can remove or neutralise the minerals present in hard water.

As you can see, there are various causes for radiators not heating up. By identifying the root of the problem, you can take the appropriate steps to address the issue effectively and reinstate your radiator's optimal heating performance.

Troubleshooting Tips

There are several reasons why radiators may not be heating up, but fortunately, there are also some simple fixes that can help get your radiators working again. In this section, we will explore two common troubleshooting methods – bleeding a radiator and balancing radiators.

Bleeding a Radiator

One possible cause of a radiator not heating up is an airlock in the system. When air becomes trapped inside the radiator, it can block the flow of water and cause the radiator to feel cold or only partially warm. 

Bleeding the radiator can help release this trapped air, allowing the flow of water to resume and the radiator to heat up efficiently. Here's how to bleed a radiator:

  1. Switch off the heating system: Before you begin, ensure that the boiler is switched off and that the heat settings have been lowered to avoid the risk of scalding.

  2. Locate the bleed valve: Locate the bleed valve on your radiator – it is typically located at the top and to one side. It should look like a small, round vent with a square nut in its centre.

  3. Prepare a cloth and radiator key: Have a cloth and a radiator key (a special key used for bleeding radiators) ready.

  4. Open the valve: Slowly insert the radiator key into the bleed valve and gently turn it anti-clockwise, allowing the trapped air to escape. You will hear a hissing sound as the air releases.

  5. Close the valve: Once water begins to leak from the valve, immediately close the valve by turning the radiator key clockwise. Be prepared for a small amount of water to escape when doing this, and use the cloth to mop up any spills.

  6. Restart the heating system: Turn your boiler back on, and wait for the system to heat up. Check if the radiator has warmed up properly.

If the radiator still doesn't heat up, you may need to consult a heating engineer to investigate further.

Balancing Radiators


Sometimes, the issue may not be airlocks but an imbalance in the system. When radiators are not balanced correctly, some may heat up faster, while others remain cold. Balancing the radiators can help ensure that heat is equally distributed throughout your home. The process involves adjusting the valves on each radiator, and while time-consuming, it can be done without professional assistance. Here's how:

  1. Turn off the heating system: As with bleeding, ensure your boiler is switched off before beginning the process.

  2. Set the thermostat: Set your central heating thermostat to a high temperature, such as 25°C, to ensure that the boiler will continue to supply heat while you're balancing the radiators.

  3. Find the lockshield valve: Locate the lockshield valve on each radiator. It is usually found on the opposite side of the radiator from the thermostatic valve and is covered by a plastic cap.

  4. Open the lockshield valve: Remove the cap from the lockshield valve, and using an adjustable spanner, open the valve fully by turning it anti-clockwise.

  5. Turn the heating back on: Switch the boiler back on and wait for the radiators to warm up. Check which radiators reach their desired temperature first.

  6. Adjust lockshield valves and thermostat: Once you have identified the order in which the radiators heat up, turn the heating off. For each radiator that is heated up first, close the lockshield valve by turning it clockwise, then open it by a quarter to half a turn. Do this for all the radiators moving from the fastest to warm up to the slowest to warm up. Finally, return the thermostat to your normal heat setting.

  7. Check the results: Turn the heating system back on, and observe whether the radiators heat up more evenly.

By following these steps to bleed and balance your radiators, you can help resolve common issues related to radiators not heating up. If you are still experiencing problems, it may be necessary to consult a heating engineer for a system inspection or a power flush to remove debris and sludge from your pipework.

Heating System Components

Central Heating System

A central heating system is composed of several key elements that work together to provide even warmth throughout your home. These elements include the boiler, radiators, pipework, and associated controls such as thermostats and timers. It is essential to maintain each component to ensure optimal performance and prevent any issues, such as radiators not heating up.



Combis or combination boilers, combine all components and aspects of a heating system (central heating and hot water production) into one succinct and powerful unit.

Their economic size, quick flow rates and dual functionality means combis are extremely efficient and effective when heating a multitude of property sizes, being best suited for small to medium sized homes with 1-2 bathrooms.


System boilers perform best in homes with a high hot water demand, specifically either larger properties with a higher number of residents or properties with two or more bathrooms. 

System boilers store hot water in a separate cylinder which provides constant flow access but requires additional (minimal) storage space.

System boilers can service multiple flow outlets at one time, meaning no one in a larger home would be standing around waiting for a shower.

Heat Only

A heat only boiler provides the heat for a home's central heating system and hot water cylinder. A heat only boiler is suited to servicing larger properties with multiple bathrooms/radiators or a business premises with a high water demand. 

Heat only boilers do require sufficient installation space within a property, as they use two storage tanks (feed & expansion) as well as the aforementioned hot water cylinder. 

Although a combi is generally considered more space saving, a modern heat only boiler is still compact and can supply more bathrooms with hot running water than a combi can.

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A thermostat plays a crucial role in regulating the temperature of your heating system. Wireless thermostats offer flexibility for homeowners, allowing them to control the heating remotely. It is important to ensure that your thermostat is correctly installed and calibrated. If you experience issues with your heating system, double-check that the thermostat is set to the appropriate temperature, and there are no problems with its wiring or connectivity.


A timer grants homeowners the ability to schedule their heating system's operation, enabling them to choose when it turns on and off. This level of control is beneficial for energy efficiency, ensuring that the heating system only works when needed. Ensure that the timer settings align with your desired heating schedule, and familiarise yourself with how to amend the settings if necessary. In the case of mechanical timers, check that the timer pins are correctly engaged, and replace worn or damaged components as needed.

Understanding the various components of your heating system and maintaining them properly can help avoid issues like radiators not heating up. Regular servicing by a qualified professional is recommended to keep your central heating system in good working order, ensuring the comfort and warmth of your home.

Professional Assistance and Maintenance

Sometimes, DIY solutions might not be enough to get your radiator working properly. In such cases, it's best to seek professional assistance and invest in regular maintenance to ensure your heating system functions efficiently. The main services you may require are Power Flush, System Filter Replacement, and Heating System Service.


Power Flush

A power flush is a process that involves cleaning the central heating system, removing any build-up of sludge, rust, and debris. This process can significantly improve the efficiency of your radiators and prolong the life of your heating system. A professional service provider will typically use a powerful machine to pump a chemical solution through your system, dislodging any dirt and contaminants. They will then flush clean water through the pipes, leaving your system free of blockages and able to heat up properly.

System Filter Replacement

Over time, your heating system's filters may become clogged with debris, leading to radiators not warming up evenly or not working at all. To address this issue, you could consider having the system filters replaced. A professional service provider will inspect the filters, assessing their condition and determining if they need to be replaced. If the filters are no longer effective, they'll fit new ones, ensuring that your heating system works efficiently and consistently.

Heating System Service

A comprehensive heating system service is essential for maintaining the efficiency and longevity of your radiators. This service includes checking the entire system for corrosion, leaks, and any other issues, as well as inspecting boiler components and controls. The service professional may also perform radiator bleeding and balancing, valve maintenance or replacements, and checking the pressure within the system.

Regular servicing and maintenance by a professional can help address issues with radiators not heating up, as well as prevent future problems. So, investing in these services will not only keep your radiators in optimal condition but also save you time, money, and inconvenience in the long run.

Preventative Measures

Regular Checks

One of the best ways to avoid radiator issues is to perform regular checks. Routinely inspecting the system, from the thermostat to the radiator valves, can help detect problems before they escalate. For instance, monitor the pressure dial on your boiler to ensure it remains between 1 and 2 bars. If the pressure is too low, you may need to use the filling loop to add water to the system and increase the pressure.

During the summer months, it's advisable to switch your heating system to summer mode. This will allow the boiler to continue working, but only provide hot water, giving radiators a break and helping to prevent problems associated with inactivity.

Heating System Efficiency

Maintaining your heating system's efficiency can help avoid radiator issues in the long-term. Be proactive about addressing potential water leaks or thermostat issues. If you notice a drop in your system's performance, it might be time to check for leaks or get your thermostat repaired.

Bleeding your radiators regularly can also prevent airlocks, which might lead to their poor performance. To do this, locate the bleed screw on each radiator and use a radiator key to release trapped air, ensuring the system is switched off while doing so. It's essential to re-check the boiler pressure after bleeding to ensure it remains within the required range.

Optimising your heating system's efficiency not only prevents radiator issues but also saves energy consumption, leading to cost savings on your utility bills. By following these preventative measures and conducting regular checks, you can greatly reduce the risk of radiators not heating up and keep your heating system working efficiently.

Additional Considerations

Radiator Sizes

When dealing with a radiator that is not heating up effectively, one factor to consider is its size. Radiator sizes can greatly impact the efficiency and heat output of your central heating system. To ensure optimal performance, it's essential to select the appropriate size for your space. Smaller radiators may struggle to warm larger rooms adequately, while oversized radiators can lead to unnecessary energy consumption and higher costs.

To determine the correct size for your radiator, consider the room's dimensions, insulation, and heat loss rate. Properly sizing your radiator ensures that you get the most out of your central heating system, maintain a comfortable temperature, and benefit from improved energy efficiency.

New Radiators

If you've checked thermostatic valves and other potential issues, and your radiator is still not heating up, it might be time for a new radiator. In general, radiators should be replaced every 15 to 20 years. Upgrading to a new radiator can offer multiple benefits, such as improved efficiency and modern features like built-in thermostatic valves.

When shopping for a new radiator, look for energy-efficient models that provide the necessary heat output for your space. Additionally, consider the material of the radiator: aluminium and steel are popular options, each with its own pros and cons. Aluminium radiators are known for their quick heat-up times and lightweight design, while steel radiators boast durability and a range of styles to complement your home's décor.

Lastly, when installing your new radiator, ensure proper pipework and valve functioning. By choosing the proper radiator size, material, and set-up, you can maximise efficiency and keep your home comfortably and consistently heated.

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Frequently Asked Questions

Why are my radiators not getting hot?

Radiators might not be getting hot due to trapped air requiring bleeding, a malfunctioning boiler or central heating pump, thermostatic radiator valves that might be stuck or set too low, or the central heating system having sludge or rust which causes blockages.

Why is my heating on but radiators are cold?

If the heating is on but radiators are cold, it could be due to a faulty central heating pump, issues with the boiler, a closed shut-off valve, or blockages in the pipes or radiators.

Why is my radiator not heating up despite being bled?

If a radiator isn't heating up even after being bled, the issue could be more than trapped air: blockages due to rust or sludge, faulty or stuck thermostatic radiator valves, or a malfunctioning central heating pump might be the cause.

Why is my radiator cold even after bleeding?

A radiator remaining cold after bleeding might indicate underlying issues such as blockages, malfunctioning valves, or problems with the central heating system like the boiler or pump.

Why are all my radiators not working after bleeding?

If all radiators remain cold after bleeding, it suggests that there might be a problem with the central heating pump, the boiler could be off or malfunctioning, or there could be an issue with the thermostat or the entire central heating system.

What happens if you bleed a radiator with the heating on?

Bleeding a radiator with the heating on can lead to more air being drawn into the system, and it's generally recommended to turn off the heating and allow the radiators to cool before bleeding to prevent this issue and avoid potential scalding from hot water.

Why are my radiators not working but hot water is?

Radiators not working while there's hot water usually indicates an issue with the central heating circuit rather than the boiler. This could be due to a faulty motorized diverter valve that prioritizes hot water over the radiators, a malfunctioning central heating pump, thermostat issues, or blockages or air in the central heating circuit.

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Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.