Are your radiators not heating up properly? Do they feel cold to the touch?

Don’t worry. This is an easy fix. It is time to bleed the radiator.

Bleeding the radiator is a simple job that could keep your home comfortably warm. Moreover, it can also save money on your bills because radiators work with boilers. As a result, you are paying for the energy consumed by the boiler but aren’t able to enjoy the toasty temperature.

Our guide to bleeding radiators can help you to find answers to the majority of your questions.


What is Radiator Bleeding?

What is Radiator Bleeding?

The radiators are designed to heat the air in two ways: radiation and convection. Radiators work similar to the heat from an open fire or a stove. Through electromagnetic waves, a radiator transfers heat to the air using radiant energy. The hot air rises when the air next to a radiator is heated with radiant energy. Thus, it pulls the cool air through the radiator and makes the cycle of air movement.

Over time, air can flow into the central heating system and rise to the surface of the radiators. It is especially those fed by downpipes and furthest away from the boiler. This bubbled-up air impacts the radiators to work efficiently in heating the room.

You hear a gurgling or clucking sound coming out from your radiator when this air gets trapped. These sounds are caused due to vibration leading to irregular air pressure.

Trapped air prevents the entire radiator from heating the air properly. In addition, it also oxidizes the pipes.

Sometimes, the radiator takes a lot of time to reach the target temperature or it may leave some cold spots. That is when you will need to bleed the radiator, irrespective of the kind of radiator you have. When you bleed a radiator, you release this air trapped within the system. It is a common problem in unvented heating systems.

When to bleed a radiator?

In every season, radiators will end up with air in the pipes. You may need to bleed this air from them to maintain consistent heat in your house. However, bleeding the device at the start of the heating season can help you prepare for the winter.

Here are a few signs/reasons to bleed your radiator:

Radiator hot at the top, cold at the bottom

Radiators cold at the bottom yet hot at the top indicate that the flow of hot air has been blocked or diverted. As a result, it is preventing it from touching the entire radiator. Sometimes, it is already hot around the water intake and exit points at the bottom. Here, the problem lies generally in the centre and at the bottom of the radiator.

Most of the time, it is the built-up sludge. Radiators are made of iron and steel. So, it creates iron compounds as the water passes over it. It starts with small amounts of accumulation with more material multiplying the grime.

Radiator cold at the top

A properly functioning radiator means it should feel hot everywhere when you turn it on. The temperature at the bottom of the radiator should be the same as it is at the top or any other place. However, you may have turned on central heating for a while, but the radiator is still cold at the top. The most likely reason for this problem would be the trapped air. Air does not conduct heat as effortlessly as water, and the air is not heating up. Thus, the top of the radiator seems cold.

One radiator not working up 

If one radiator is not heating efficiently in your home, check if just a part or the whole of it is cold. If the whole radiator feels cold, you need to check if the valves on both sides of the radiator are switched on. This may sound like a basic step, but it is best to cross out that possibility.

If the radiator is partially cold, determine where it is not heating. Trapped air will keep the top part of the radiator cold. However, if it is cold at the button, it may have accumulated some debris. 

Radiators with rattling sound

If you hear a gurgling sound of a kettle about to cook, the source of the noise is usually not the boiler. It is anywhere else in your heating system, such as the radiators or pipes. Air stuck within the device is the most common source of a loud radiator when the heating is turned on. It is essential to address this problem as soon as you become aware of it. Bleed the radiators to get rid of this problem.

Preventive Bleeding 

Preventive bleeding is important to avoid any major problem in the radiator. It is essential to bleed the radiator once a year, before the start of the cold season. As a result, this should be a component of the yearly heating maintenance schedule.

You can bleed the radiators one by one, from the bottom to the top level. But, it depends upon the configuration of the heating system. If you find yourself having to refill or bleed the heating tank more frequently, there may be leakage. You should get it repaired by a heating technician.

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How to bleed a radiator?

If you see any of the above signs or want to have preventive bleeding, it is quite easy, and you can do it independently.

If you are planning to release air from the radiators, you will require these tools with you:

  • A radiator bleed key/radiator key - to open the radiator vent valve (you can find it at most hardware stores)

  • A cloth or towel to collect drips.

Here is a step-to-step guide on how to bleed a radiator:

Step 1: Switch on the heating system

Before bleeding, switch on the heat and allow all radiators to warm up. This creates pressure in your radiator, forcing the excess air out. You can use the quick actions if you have tado° devices, turn on all SRTs in the home, and bleed the radiators.

Step 2: Determine which radiators require bleeding

Check each radiator for cold spots in your home. What are the signs of a radiator that needs to be bled? Trapped air is the most definite cause if you experience any of the following conditions:

  • hear gurgling sounds

  • the heater takes a long time to heat up

  • or there are cool spots

This is stopping hot water from filling the radiator; you will need to bleed it. Since the radiators will be hot, proceed with caution. We recommend you wear a pair of thin gloves so that you do not burn yourself.

Step 3: Switch off the central heating system 

Don't forget to turn off the central heating before bleeding the heater. If your heating is on, you risk scalding yourself and flooding the floor.

Step 4: Set up the field

Stained water comes out when bleeding an old radiator. Put the towels on the floor and save the cleaning job eventually.

Step 5: Open the radiator bleeding valve

Before moving to bleed the radiator, you need to remove the bleeding valve. The type of radiator head will determine the process of unmounting the radiator. Put the radiator bleed into the bleed valve. You will find the bleed valve on the side at the top of the radiator. It appears to have a square surrounded by a round hole. You will feel the lock together until you insert the radiator key into the radiator bleeding valve. Turn the valve anti-clockwise until you hear a hissing sound as the air leaves. Keep a safe distance from the escaping air because it may be hot. If you don't have a radiator vent key, you can use a flat-headed screwdriver on modern radiators.

Step 6: Bleed the radiator

A quarter to half turn will suffice. Never open the valve completely. It will let the water rush out until you bleed air from the radiator. Continue to hold the radiator bleed key until the air stops coming out. When only water drips from your radiator, you've finished the bleeding process. Turning the bleed valve clockwise seals the radiator; be careful not to over-tighten. Water can be released as a 'jet' through modern bleed valves. Turn your bleed valve key with caution, and be ready to close the bleed valve quickly.

Step 7: Repeat the procedure on all radiators

All the radiators in your home need bleeding. Because the air rises through the system, start on the ground floor and work your way up.

Step 8: Check the pressure of your heating system

After bleeding all of your radiators, you'll need to re-pressurize your heating system. When you bleed a heating system, some water is always lost. If it amounts to a huge quantity, the system may struggle to heat the top floors of your home. At times, the central heating system may fail completely.

For accurate system water pressure, the needle gauge will highlight the green area. If it is yellow, the system must be re-pressurized. To do so, identify the central filling loop attached to your boiler. It resembles a tap and is attached to your main water supply.

Theoretically, the pressure in a typical family home ranges between 1.0 and 1.5 bar. Always turn on the water and gradually adjust the pressure. There is also a bleed tap in the unlikely event that you apply too much pressure and the needle turns red.

How to bleed a radiator without a key?

Radiator bleed valves come in a variety of shapes. Some are in the shape of square nuts. And, the radiator key is essentially a socket that aligns over the nut and is connected to a handle. If you happen to lose this type of key, attain your socket wrench set. Then, select the socket that fits over the plug. We can also turn this type of plug with a spanner or pliers. 

Can you bleed a radiator when the heating is on?

No, it would help if you didn't bleed the radiator when the heating is on. Before bleeding from a radiator, remember to turn off the central heating. Check how quickly you can turn off all smart radiator thermostats at once in the home if you have tado° devices. When the heating is on, you cannot bleed a radiator because it may be too hot to touch. Allowing air to escape while the pump is running will only draw more air into the system.

How does the air get into the heating system?

There are several ways to introduce air into a central heating system. This may occur when extra water enters the expansion tank or when maintenance work is performed. The pump's movement could also create it as it turns. Leaks are frequently the source of air buildup. This can occur if the boiler is frequently re-pressurized.

How to maintain optimal heating?

For ensuring perfect, and healthy living, it is vital to maintain the room temperature. There are different room temperature requirements. On the one hand, you need an ideal temperature to have a good night’s sleep in the bedroom. Contrarily, a standard temperature in the living room can maintain and boost productivity.

Maintaining Optimal Heating Using Smart Thermostats

A smart thermostat automates your home's heating and cooling system. It provides maximum comfort while also saving you money and energy. A smart thermostat is controllable via a system panel, an app, or even a voice assistant. It's advantage lies in its ability to understand the household's behaviours. As a result, it adjusts heating and cooling based on when a home is occupied or is about to get occupied.

tado° can manage almost any type of heating system. The precise way tado° controls your system is determined by the type of heating system you have. tado° devices give a smart level of control over your central heating system.

Maintaining Optimal Heating Using Smart Radiator Thermostat

Advancements in technology have replaced conventional radiators with smart radiator devices. Smart radiator devices allow you to monitor each radiator in your home using an app. This application can be used on your smartphone, tablet, or smartwatch. You can select a certain temperature, set schedules, or switch them off, no matter where you are. 

Smart Radiator Thermostats are simple and cost-effective to upgrade your heating controls. Also known as Smart TRVs, they are more advantageous and easier to set up than traditional TRVs. Implementing smart radiator thermostats enables Room-to-Room Heating Control. This is a critical wave for saving money with smart heating. It enables different schedules for different rooms based on usage. Not only convenient, but the smart radiator thermostats also provide energy efficiency.

A central room thermostat controls the heating for the entire house. It can be either wireless or wired. With tado°, you control the boiler by replacing the central thermostat. In addition, Smart Radiator Thermostats help easy heating control in individual rooms.


Bleeding the radiator helps to keep them in good working order. Try bleeding them at least once. It causes the radiator to begin heating up and emitting heat.

Implement Smart Thermostat and Smart Radiator Thermostat for your heating system. Control the heating in each room separately. tado° Smart Schedule feature allows you to plan the temperatures in time frames. Now your room will be perfect with the temperature just as you want in a few taps. Energy Saving will be easier. Say Hello to a better home with tado°.