How To Bleed A Radiator

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The pressure in a hot boiler system changes over time. On every boiler, you can find a gauge that displays the pressure value, and we can regulate it by using the radiator valves. Deciding what to set the pressure for is a little more complicated. However, the section following the one on how to bleed a radiator includes a brief explanation of optimal boiler pressure. Plus some common practices to achieve it when preparing for winter.

Hot water boiler systems are pressurized. Also known as a closed-loop system, all this means that they need to be full of water to work at their best. For clarity, water must flow from the bottom to the top of the piping system. And the pressure is what you get when you fill the piping system at full capacity. But if air gets in the pipes, the pressure goes down. So, we bleed a radiator to fix pressure. The symptoms of this are explained in detail in this article by Easy Boiler Company - Is your radiator cold at the bottom and warm at the top?

How To Bleed A Radiator Step By Step


  • First of all, make sure to switch off the boiler. Even knowing how to bleed a radiator perfectly cannot protect you from a hot water spill if the boiler is on. Only proceed with cold water in your pipes. During winter, give plenty of time to your radiators to cool down.

  • If you do not have a radiator key, buy one at your local DIY shop. While you are at it, consider getting safety gloves, goggles, and clothing if you have not any at your place to bleed the radiators safely.

  • Inspect the radiator bleed valve. If you notice a broken valve, you can find a self-drilling radiator air vent to fix it. In any case, make sure that the new air vent is closed before you start drilling it inside your radiator. Of course, this is not a standard procedure. So, follow the instruction manual that comes with the self-drilling air vent to the letter.

  • When you are ready, put a towel on your floor, just in case you spill any water during the bleeding.

How To Bleed A Radiator Like A Pro

  1. Always start at the lowest point in your property. In other words, bleed a radiator on the first floor before bleeding another on higher floors.

  2. Open the thermostatic radiator valve if you have one. Otherwise, check the lockshield and make sure it is open. That is the knob with the plastic cap that you find at the lower end of the radiator. Only open the thermostatic valve if you have it.

  3. Find the bleed vent on the radiator. Usually, it is in the upper corner. But depending on the model, the vent may be in a different location or have a peculiar shape-some have even a directional nozzle to avoid spatters on the walls.

  4. Place the radiator key over the vent and turn it slowly. At this point, you should also have a tissue underneath the vent to prevent spilling water on the floor. Unwanted air will come out hissing. Shortly after the hiss dies down, water will come through.

  5. Turn the vent off when the water stream is regular. For clarity, any residual air will create a sluggish stream. But water will come out consistently as soon as there is no more trapped air.

The Perfect Boiler Pressure

A boiler pressure between 14 and 22 psi (1 and 1.5 bar) is recommendable. With this in mind, the boiler's manual may suggest another value. If your manual recommends another pressure value, please stick with the instruction manual.

Different models may have varying pressure readings when active. Then again, some reach 29 psi (2 bar) when heating up.

Almost all boilers need technical assistance when the pressure stays below 7 psi (0.5 bar) consistently. In this case, the problem may not be about how to bleed a radiator correctly but rather a technical issue. The gauge could also have broken down.

Why Optimal Pressure Is Important

When the boiler pressure is right, the radiators heat up properly. This means that they are hot or warm at the top and at the bottom. When you turn on the heating system and the temperature across the radiator body is uneven, the pressure is too low and you need to repeat steps 1-5 in the section How to bleed a radiator like a pro.

Air bubbles also cause your heating bill to go up which is not helping you save money on your energy bills. After all, when the radiators do not heat correctly, the room remains cold. The more time you keep the heating system on to compensate for inadequate heating capacity, the higher the expenses. By contrast, optimal boiler pressure reduces energy costs.

Making Your Boiler Last Longer

Low pressure happens over time and after a recent radiator bleeding procedure. In rare cases, it can indicate you have a leak in your system. Conversely, high pressure could damage the boiler or your system. And you should bleed the radiators when this happens. In the end, you have not just learned how to bleed a radiator because you now know how to regulate your boiler system pressure as well.

To top up boiler pressure, please check your manual. Usually, the instructions involve restarting the boiler. But you might have to close some inner valves as well. Or contact a boiler technician.

Boiler Maintenance Tips

If you need to learn how to bleed a radiator, you may find these boiler maintenance tips valuable.

  • Typically, it is a good idea to check boiler pressure during fall. In winter, make sure the pressure gauge works. If you see that the device is stuck and the reading does not change when you turn the boiler off, you do not have to call for an emergency repair at once. Place a hand on each radiator and make sure that they heat up evenly. Eventually, contact an engineer for a repair in spring. So, you will not have to wait for the busy technician or lose working hours over a simple replacement.

  • If the radiator vent is difficult to open, do not force it. Instead, seek the guidance of a plumber to avoid damaging the radiator.

  • Some boiler models need you to top up the pressure after bleeding the radiator. Please, consult your instruction manual for more info.

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