How to Repressurise a Boiler

November 11, 2022
A close of someone pointing to a boiler pressure gauge.

If your boiler has stopped working and your home has been left without any hot water or central heating, there could be a problem with your boiler pressure. Learning how to repressurise a boiler is a helpful skill and will save you the time and cost of calling out a Gas Safe engineer to fix the problem for you.

In this article, we will be sharing how you can repressurise your boiler safely and easily.

If Your Boiler Has Low Water Pressure

If you suspect your boiler’s pressure problem is due to low water pressure, the first thing you should do is look at the water pressure gauge located on the front of your boiler system. Depending on the type of boiler you have, this pressure gauge may look slightly different. However, if you cannot find it you should refer to your boiler manual.

Digital Pressure Gauge: for boilers with digital pressure gauges, boiler pressure is often represented by bars. If your boiler gauge shows less than one bar, this is a common sign that your boiler has low pressure. Some boiler systems indicate low pressure by flashing a pressure warning reading on the display screen.

Hydraulic Pressure Valve: if your boiler has a hydraulic pressure valve, you will find the boiler reading on a dial. This dial will have red sections that indicate both high and low pressure. If the needle is on the left hand side of the boiler indicator, the pressure is too low and if the needle is on the right hand side, then the water pressure is too high.

We highly recommend you check your boiler’s water pressure every couple of weeks, especially during the winter months, as you don’t want to wake up to no central heating or hot water.

What is Good Water Pressure?

When your boiler has healthy water pressure, you will see a reading between one and two bars. Anything below one bar is low and anything above 2 bars is high.

Please Note: high water pressure could indicate that your central heating system has overfilled with water and can be dangerous to fix yourself. If the water pressure on your boiler is measuring high, it is best to call our expert boiler engineers to come and fix the problem.

How Often Should You Repressurise Your Boiler?

You should only repressurise your boiler when it’s needed. For example, when the boiler pressure level is too high or too low. If you are having to repressurise your boiler on a regular basis, this could signify a more serious problem such as a leak within the system. To avoid expensive repairs, it’s important to give our team a call. We can diagnose the problem and carry out the necessary repairs before the issue worsens.

How to Repressurise Your Boiler

Now that you know a bit more about boiler pressure, what’s normal and what’s not, it’s time to learn how to repressurise your boiler. Our experts talk you through the process from beginning to end so you can restore your boiler’s pressure and get on with your day.

Always Check Your Boiler’s Manual

First things first; always check your boiler manual. Every boiler model is different, so the process for repressurising your system may be a little different to what you’d expect. Some boiler manufacturers even post instructional videos on their website explaining how to repressurise your boiler system. So, it can be helpful to check!

How to Repressurise a Boiler with a Repressure Key

Below we share 9 quick and easy steps to repressurise your boiler system with a repressure key.

  1. Switch Off Your Boiler
    Before commencing any work on your boiler, it is essential to turn the system off and give it plenty of time to cool down. Once cool, you can begin the re-pressurising process.
  1. Find the Internal Filling Key
    No, this isn’t a key that you’ll find stored in your drawer of knick-knacks. The internal filling key can be found on your boiler system. What you are looking for is something that looks like a plastic tray. You should be able to slide this open and find the internal filling key inside.
  1. Find the Two White Arrows
    The filling key should have two white arrows near its base. These arrows need to be lined up to the key in the manifold.
  1. Find the Manifold
    The manifold is a part of your boiler made from black plastic. It is connected by your cold mains and goes into your boiler to the central heating system within the appliance.
  1. Find the Padlock Symbols
    On top of the manifold, you should find engraved padlock symbols.
  1. Insert the Key into the Manifold
    You need to line up the two white arrows on the filling key and then turn the key until the arrows line up with the open position of the manifold. Next, push the key inside and rotate it to the closed position. Do this carefully and without applying unnecessary force.
  1. Let Water Enter the Boiler’s System
    Once you are sure the internal filling key is closed, turn the white plastic nut counterclockwise. You should hear water entering the boiler’s system and filling the appliance.
  1. Check the Boiler’s Pressure Gauge
    Once you have completed the above steps, you must re-check the boiler’s pressure gauge. If the process has been successful, the pressure gauge should read about 1.5 bars.
  1. Lock the Internal Filling Key
    When the boiler’s pressure gauge is reading about 1.5 bars, you have successfully re-pressurised your boiler and can lock the internal filling key, making sure the white nut is also tightened.

How to Repressurise a Boiler with a Filling Loop

  1. Always start by turning your boiler off and giving it plenty of time to cool down.
  2. Once cool, check your boiler’s filling loop to ensure both ends are attached and secure.
  3. Open the two valves. You will hear cold water entering your boiler system.
  4. Keep the valves open until you see the pressure reading on your boiler get to 1.5 bars.
  5. Then, close both valves one at a time.
  6. Switch your boiler back on. Depending on the type of boiler you have, you may need to press the boiler’s reset button.
  7. Next, undo the filling loop.
  8. Clean the filling loop and store it in a cool, dry place.

How to Repressurise a Boiler Without a Filling Key

If your boiler has a keyless internal filling loop, re-pressurising the system couldn’t be easier! All you have to do is locate the blue lever at the bottom of your appliance. Pull the lever and wait for your boiler’s pressure to rise. Once your boiler pressure has returned to 1.5 bars, you can release the lever and the process is complete!

Boiler Pressure Not Improving? Give Us a Call!

If you have attempted the above without any success and your boiler pressure has not improved, it’s best to call our team. If a boiler won’t re-pressurise, there is often an underlying issue such as a leak in the system or a faulty pressure relief valve.

Here at City Warmth, we provide emergency callouts to our customers in Brighton and Hove. All you have to do is give us a call. We will send one of our Gas Safe Certified engineers to you and they will professionally diagnose the issue and provide any necessary repairs.

For more information on boiler care, check out our blog.

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