Home Improvement

How to Repressurise a Boiler

If you’ve come home after work and noticed it’s colder than usual, there might be a problem with your heating system. Your next order of business is to check the radiators. If they’re cold in certain places only, you might have to bleed them to remove a bubble of air. But, if the entire heater is cold, then the problem is most probably low pressure in the boiler. 

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So, in this article, the Fantastic Services team will explain how to repressurise a boiler, so you don’t have to deal with this problem ever again.

So if you:

  • Own a boiler and a heating system;
  • Have been experiencing a drop in pressure in your combi boiler;

Then keep reading – this blog post has the solution!

What does a boiler do?

In general, a domestic boiler is supposed to heat water and transfer it to the radiators in your home, creating an effective heating system. The most common types of domestic boilers are: 

  • Conventional. A conventional boiler supplies the central heating system, sinks, baths and showers with hot water. Coldwater provided by the tank is heated and then stored in the cylinder until required by the taps or the heating system. Because they have a reservoir of hot water, they can supply more than one user at the same time. 
  • Combi. A combination, or combi, boiler, has the same function, only it supplies the central heating and taps with hot water directly from the water supply, without the need for a tank. The hot water is not being stored in a cylinder but is instantaneously supplied, which is perfect for a household with limited space. However, because there is no water tank, it’s hard for the boiler to provide more than one user with hot water. If two or more taps are used simultaneously, it usually results in a pressure drop.
  • System. System boilers have a hot water cylinder but no water tank. This requires less space than the conventional boiler, but unlike the combi boiler, it’s also able to supply multiple taps simultaneously. Still, the hot water supply is limited to the size of the cylinder.

Is there a drop in pressure?

To check whether there’s a drop in pressure in your boiler, find the water pressure gauge. If it reads less than 1 bar, you might have lost water from the system due to leaks or bleeding. If the pressure reads above 2.75 bar, then you may need to bleed a radiator to bring the level down. Normal pressure is around 1.5 bar.

What causes a drop in pressure?

A boiler and a heating system can stumble upon a lot of different complications. In most cases, we don’t recommend fixing those issues on your own. The most common reasons for a drop in pressure are:

  • Heavy usage. If you own a combi boiler, pressure mostly drops because of the simultaneous usage of two or more hot water taps. This is not an issue, but a frequent occurrence. It’s advisable to use combi boilers only in small households with small usage of water.
  • Leaks. Even a tiny leak in your heating system can turn into a gradual drop in pressure. Check around the pipes in your house and look for damp patches. It’s also important to check if your boiler is leaking water from any pipe. When you find the leak, and especially if you have a suspicion that the leak is within the boiler itself, immediately call a Gas Safe engineer.
  • Bleeding radiators. If you have bled your radiators recently, you may have lost some pressure. That’s because, when you do this, the air is released, which lowers the pressure in your boiler system.

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How to repressurise a boiler

Time needed: 20 minutes.

Since there are different types and brands of boilers, the first thing you should do is check your instructions manual. There is usually an explanation of how to safely repressurise the boiler by yourself. Then, just follow the instructions:

  1. Switch off.

    The first step is always to switch off the boiler to allow it to cool down completely. This is an important safety measure. Never work on a boiler that’s still running.

  2. Find the filling loop.

    The boiler filling loop is a component that provides a temporary connection to the mains in order to pressurise the central heating system. It allows for the pressure to be easily normalised. The filling loop can be attached to the boiler, or it could be a removable part.

  3. Open the valves.

    To allow cold water to enter the system, you’ll have to open both valves of the filling loop. This will start to increase the pressure gradually. Keep your eyes on the pressure gauge until it reaches 1.5 bar.

  4. Close the valves.

    Once the pressure is normal, close the valves one after the other. Remove the filling loop if it’s removable.

  5. Turn the boiler back on and check.

    Once that is done, turn on your boiler and recheck the pressure. If it stays around 1.5 bar, you’ve done an excellent job. If you’re still experiencing issues, then you’ll need a certified technician to take a look.

Don’t panic if you accidentally over-pressurise the system. The opposite process of lowering the pressure is by bleeding your radiators. It’s important to keep an eye on the pressure over the following days and weeks. If it doesn’t stay constant, then you have a more serious problem. Another drop usually means there is a leak somewhere in your piping system.

Do you need help with your boiler maintenance?

Are you experiencing problems with your boiler? Does your heating system not work the way it used to? There are a lot of things that can go wrong and most of them need to be looked at by a certified technician. 

If you don’t know how to repressurise a boiler or aren’t comfortable doing it, don’t try to fix it by yourself! And under no circumstances should you open up the boiler itself! Not only could you lose your boiler’s warranty, but it could also be dangerous, depending on the issue. Get in touch with the boiler repair specialists from Fantastic Services and let the professionals fix your problem! You can also think about getting a boiler cover and save money in the long run in case of an unexpected boiler breakdown.

Visit the main website for price rates for our professional boiler technicians!


  • The most commonly used types of domestic boilers are conventional, combination and system boilers;
  • If your boiler experiences a drop in pressure, it’s most commonly a leak in the piping system or a result from bleeding a radiator;
  • The pressure gauge gives a good understanding of the condition of your boiler – 1 bar and below is low pressure, 1.5 bar is normal pressure, 2.75 bar and above is high pressure;
  • To normalise the pressure of your boiler, you should always follow the boiler’s instruction manual;
  • Increasing pressure in the boiler is done by operating the boiler filling loop;
  • Decreasing the pressure in the boiler is done by bleeding the radiators;
  • If the problem persists even after using the filling loop, you should call a certified technician.


Have you ever needed to learn how to repressurise your boiler? What was the problem and what did the boiler technician say? Tell us in the comments!

Image source: Alexander Raths / shutterstock.com

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