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How to Repressurise a Boiler – A Complete Guide For Beginners

Man repressurising a combi boiler

Every time you find the strength to do boiler maintenance, you feel like something is going to break. On top of everything – it’s such tedious work. It is crucial to learn how to repressurise a boiler and be ready when pressure problems arise. No matter how much you dread turning valves and searching for leaks, this is one of the most important check-ups.

With the last in mind, in this article, we are going to share with you how to re-pressurise your boiler in a easy and safe way. 

How to Check Your Boiler Pressure 

To check your boiler’s pressure, first you need to locate the pressure gauge. Typically, you can find it on the front part of the appliance. There are different types of water heating appliances that have different pressure gauges. The two most popular are digital and hydraulic. 

For example, if you have a digital gauge, the pressure is represented by bars. Reading such a gauge is quite easy – if it indicates less than 1 bar, you have a pressure issue. 

Hydraulic pressure gauges, on the other hand, give you a dial reading. Generally, this boiler part has two red sections, and sometimes – a green one. When the gauge’ needle drops to the left red section, the pressure of the appliance is too low. And when it points to the right one – it’s way too high. You know what the green section indicates – the normal pressure you are looking for.

What is The Normal Boiler Pressure?

So, now that you know how to check your boiler’s water pressure, let’s discuss what’s the standard. When your pressure gauge shows a number lower than 1, your boiler’s pressure is low. And If you see a number higher than 2.5, then your pressure is too high. What you are looking for is something in the middle and that is 1.5 bars.

How to Repressurise Your Boiler Using an Internal Filling Key

Now that you know how to diagnose your boiler, it’s time for the “fun” part. Roll up your sleeves and fix the pressure issues. Before you start, we highly recommend you to find the appliances’ manual and keep it close. Sometimes there are specific instructions that apply only for this particular boiler type. 

With that out of the way, follow these 8 easy steps to find out how to repressurise your boiler:

Step 1. Locate  the internal filling key

What you are looking for is a small plastic covering that resembles a tray. Remove it to locate the internal filling key. 

Step 2. Locate the arrows of the key

Do you see the two white arrows placed near the base of the key? They need to be lined up to the key in the manifold.

Step 3. Locate the manifold

This part is made from black plastic and is connected by your cold mains. It goes into the boiler, and through to the central heating system of the appliance. 

Step 4. Locate the padlock symbols

You can find these symbols engraved next to each other on top of the manifold’s plastic. Now, it’s very important to figure out which symbol is which. That allows you to position the internal filling key the right way. 

Step 5. Push the key into the manifold 

This part is fundamental for the whole procedure. Locate the two white arrows on the key and turn them. They have to line up with the open position of the manifold. Then, carefully push the key inside and turn it to the closed position. Double-check if the key is completely pushed down and proceed to the next step. 

Step 6. Let water into the appliance’s system

Make sure that the internal filling key is closed and turn the white plastic nut counterclockwise. You should hear how the water fills the appliance. 

Step 7. Check the pressure gauge

Now that you’ve completed the above-listed steps, it’s time to check the pressure gauge once again. If your boiler successfully reached 1.5 bars – congratulations, you’ve almost resolved that issue. What you are left to do is to… 

Step 8. Lock the internal filling key

Lock the internal filling key and make sure that the little white nut is also tightened. That’s it – you are done! 

How to Repressurise a Boiler With an External Filling Loop

An external filling loop means exactly what you think it is. You can have a far easier time re-pressuring your heating appliance. Follow these steps to complete the task:

  1. Locate the cold water mains valve and the heating system’s valve. Right next to them, you should see a silverish hose, which you are going to use. 
  2. Grab the hose and connect it to each valve. 
  3. First, fully open the cold water mains valve and then the heating system one. 
  4. Keep an eye on the pressure gauge – you are looking for pressure over 1 bar. 
  5. Close both valves once you’ve reached the desired pressure. Make sure to leave the hose attached. 

How to Repressurise a Keyless Internal Filling Loop

Do you have a boiler with a keyless internal filling loop? Then consider yourself very lucky – repressuring such a boiler is quite simple. All you have to do is check the bottom part of your appliance – you are searching for a blue lever. Once you find it, pull it and wait for the pressure to rise. Once your boiler has reached a pressure of 1.5 bars, let go of the lever. 

Most Common Questions About Boiler Repressurising

How often should you repressurise your boiler?

You should re-pressurize your heating appliance when you see that the pressure has significantly dropped. Make sure to keep a close eye on your boiler. If you find yourself re-pressuring it rather too frequently, you most likely have a leak somewhere in the appliance. Postponing a necessary boiler repair can lead to serious damage, so better address the issue as soon as possible. To act proactively is your best go-to. You can preempt preventable damages to your heating system when you entrust an annual boiler check to a certified gas safe engineer. 

Is it possible to repressurise my boiler too much?

Yes, it is. To revive the situation, you’ll need to let the pressure drop a little. The simplest way to achieve this is by bleeding your radiators. You know how this one goes – get your bleed key, lay a couple of towels or rugs under the radiators. Open the bleed valve slowly. Let some water drip out and ta-dah – you fixed the pressure issue! 

My internal filling key got stuck. How can I fix it?

Take a deep breath and DON’T touch the key, as it can lead to over-pressurizing your boiler. The only thing that you can do in a situation like this one is to call a professional to fix it for you. 

The boiler pressure is not improving. What do I do now?

You’ve followed the above-listed steps and you still can’t re-pressurize your boiler? Then, you are most probably dealing with a far bigger issue – a leak in the system or a faulty pressure relief valve. My Plumber’s gas safe certified engineers are ready to handle any emergency boiler repairs in London. All you have to do is contact us and ask for a professional to resolve the issue as soon as possible. 


  • The key to a well-performing boiler is regular check-ups and taking the necessary maintenance measures, which include re pressurising your appliance when needed. 
  • Re-pressuring is not an impossible task, however, it can be a hard one, especially if you have an internal filling key. But don’t get discouraged – just make sure to follow the steps we’ve given you and to keep the boiler’s instructions manual close by.
  • If you’ve tried everything we described in this article, and nothing helps, we suggest hiring a certified technician to inspect your water heating appliance.

Image source: Yevhen Prozhyrko / Shutterstock

How to Repressurise a Boiler – A Complete Guide For Beginners

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