Radiators Not Heating Up: How to Fix?

Radiators are key to keeping your home warm, so it’s important to make sure they work properly. When they stop heating up as they should, it can make your home cold and uncomfortable.

This simple UK guide explains how to spot and fix common radiator problems. You’ll learn about what can cause issues, how to check which part might be at fault, and when it’s best to call a professional for help.

By understanding what causes radiator problems and how to prevent them, you can keep your heating system running efficiently and avoid bigger issues later on.

Main Reasons for Radiator Issues

Cold Radiator

If your radiator stays cold, there are a few common reasons. The valve might be turned off, stopping hot water from flowing through.

Air could also be trapped in the pipes, or sludge might have built up inside the radiator, blocking the heat. Checking and cleaning your radiators regularly helps prevent these problems.

Air in the System.

Trapped air can cause your radiator to heat unevenly, with some parts hot and others cold. To fix this, use a radiator key to bleed the radiator and let the air out.

This helps the hot water move properly and makes sure the radiator heats evenly.

Radiator Valve Issues.

Radiator valves control how much hot water flows through your radiator. If the valve gets stuck or blocked, the radiator won’t heat up properly.

Remove the valve head and check the small pin underneath, if it’s stuck, gently press it to free it and help the water flow again.

Trapped Air

Trapped air is one of the most common reasons for a cold radiator. Air can build up in the system and block hot water from flowing through the pipes. To fix this, you’ll need to bleed the radiator.

If your radiators make gurgling or bubbling noises, it usually means air or trapped water is stuck inside the system. This stops hot water from flowing properly. Air pockets or bits of debris inside the pipes are often to blame.

Use a radiator key or flat-head screwdriver to open the bleed valve slightly. Keep a cloth or small container underneath to catch any water that leaks out. You’ll hear the air hissing as it escapes — when water starts to trickle steadily, close the valve again.

After bleeding, check your boiler pressure. Letting air out can sometimes lower the pressure, so top it up if needed. Doing this helps your heating system run smoothly and evenly.

Other Causes For Cold Radiators

When radiators stop heating up properly, it’s usually down to a few simple things: trapped air, dirt or debris, rust and sludge, or limescale.

Knowing what’s causing the issue helps you fix it faster and avoid repeat problems.

Debris and Dirt

Over time, bits of dirt and debris can build up inside your central heating system. This can block the flow of hot water and stop your radiators from heating up properly.

One of the best ways to fix this is by having the system flushed. A heating engineer can do this by connecting a special machine that uses water and cleaning chemicals to remove the buildup. You can also check and clean the radiator valves yourself, as this often helps improve water flow.

Rust and Sludge

Rust and sludge form when the inside of a radiator starts to corrode. This can block the water flow, make the radiator heat unevenly, and even cause leaks if left untreated.

You can slow this down by adding a chemical inhibitor to your system, which helps prevent rust from forming. If the damage is already bad, replacing the radiator might be the best option. Keeping your system protected helps extend its life and saves you money long term.

Limescale

If you live in a hard water area, limescale can build up inside your heating system. This mineral buildup reduces heat output, makes your boiler work harder, and increases energy bills.

To deal with it, you can add a limescale inhibitor to your heating water or install a water softener to reduce minerals in your supply. Preventing limescale keeps your system efficient and helps avoid expensive repairs.

Troubleshooting Tips

When your radiators aren’t heating up, there are a few easy things you can try before calling a professional.

The two most common fixes are bleeding the radiators to remove trapped air and balancing the system so heat is spread evenly around your home.

Both can make a big difference to your heating performance.

Bleeding a Radiator

Possible reasons for needing to bleed a radiator include trapped air inside the system, radiators feeling warm at the bottom but cold at the top, gurgling noises, or uneven heating throughout your home.

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

Possible reasons for needing to balance your radiators include uneven heating between rooms, radiators warming up at different speeds, recent changes to your heating system, or parts of the system being drained and refilled.

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.

Other Possible Reasons

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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References
https://iheat.co.uk/boiler-help/different-types-of-radiators