How to Repressurise Worcester Combi Boiler That Has Low Water Pressure

James Elston
Written by James Elston
Updated on 4th December 2023
Posted on 3rd December 2023
How to Repressurise Worcester Combi Boiler That Has Low Water Pressure

How To Repressurise Worcester Combi Boiler Showing Low Water Pressure

worcester bosch logo

Worcester bosch combi boilers have been very popular in the UK, and it has been providing excellent service to customers for several decades.

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To work efficiently the Worcester combi boiler needs to operate on a standard pressure, between 1/ 2 bar, and 1.5 bar is the optimum Worcester boiler pressure level.

So, the pressure of the combi boiler needs to be topped up with cold water through the mains at some point in their lifetime and here is how to repressurise your Worcester boiler.

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When to increase Worcester boiler water pressure

worcester boiler pressure gauge

However, while operating the combi boiler, if you notice that the pressure gauge or indicator has dropped down to the red zone, then you must repressurise it immediately.

It might happen when your system is not heated properly, has a leak from the expansion vessel or commonly happens after removing a radiator.

Worcester Bosch has been awarded the Which? Awards for the last 10 years in a row, giving trust and fantastic reviews online. You get get a new Worcester Bosch boiler, including full boiler installation online now With Boiler Central

Check if you have the Worcester Bosch intelligent Filling system on your boiler

One thing to note is that the new range of Worcester Bosch boilers has the option to have an intelligent filling system. This means that the boiler will repressurise itself automatically as and when needed. Every Worcester Bosch 8000 combi boiler has this built in as standard.

If you have a Worcester bosch 4000 combi boiler then you can choose this as an optional extra. If you do have this system then make sure that you are not trying to top up the water pressure yourself.

Too see the whole range available of the brand new Greenstar range and how much each boiler costs, check out our latest Worcester bosch boiler prices page for a comprehensive overview of the latest models from this top boiler brand.


Increase pressure of a Worcester boiler with an internal filling key 

The internal filling key is designed to lock and unlock the unit. It is basically made of plastic.

Here are the steps to repressurise the Worcester combi boiler using an internal filling key. If you are seeing a Worcester bosch error code that means low pressure in the boiler, then this will sort that out.

You can then reset the boiler if required and then your boiler should be back up and running at maximum efficiency, however, if your pressure keeps dropping then you may need to get a boiler service.

How to top up your Worcester Bosch boiler pressure


worcester 2000 boiler pressure

⭐ Step 1:

Locate the internal filling key properly and place it accordingly.

Check under the Worcester combi boiler, and you will find out a white plastic tray. Then, you will just need to locate the key by removing the tray.

⭐ Step 2:

Check out the white arrows which are pointing upwards close to the base of the key.

There, you will need to locate the arrows. After that, line up in the manifold.

⭐ Step 3:

Locate the manifold of your boiler.

It is basically made of black plastic, and it is linked to the cold mains inside the boiler through to the central heating return.

⭐ Step 4:

Locate the padlock symbol of your boiler. On the manifold plastic, the padlock symbol is located next to one another.

So, you can identify what and which will you need to perform the internal filling key properly and to position it correctly to carry out the procedure onwards.

⭐ Step 5:

worcester 400 combi boiler pressure

In this step, you will need to push the key into the manifold.

Find the white arrows of the key and line them up with an open padlock symbol which is positioned on the plastic of the manifold.

Then, push the key inside of the tubing and move it to the closed padlock symbol position. It is essential, and you must make sure that the key is pushed snugly with the manifold.

⭐ Step 6:

Make sure not to allow water to enter into the system.

When the internal key is placed in the closed position, you will need to start turning the white plastic nut with anticlockwise moves.

Then, you will begin to hear the sound of filling the hot water into the heating system.

If this doesn’t work, you may need a new boiler. If you do, find out how much a new boiler costs now a get a fixed price quote online.


⭐ Step 7:

Now, start monitoring the boiler pressure.

When the water is entering the system, you should keep an eye to the pressure gauge looking at the front side of the boiler.

When it reaches the standard pressure indicator of 1.5, then you will need to tighten the white plastic nut until the water stops entering into the system.

⭐ Step 8:

Now, remove the internal filling key from the system. For this, you will need to turn the key back to the locked padlock symbol position.

While removing the key from the manifold, you would notice a few drops of escaping water. That’s good and normal.

If you find the water is dropping continuously, then you can check the previous nut to see whether it was tightened properly or not.


What will you do if the needle raises too high on the red section? 

Firstly, don’t get anxious about it.

Just conduct an easier fix and bleed a little bit of air from the radiators.

You may require to repeat the process if the pressure drops again.

What would you do if the key gets stuck? 

If this did occur, don’t move the key; it could eventually lead the boiler to be over pressurised.

Then, it may cause damage to the unit. In that case, you may need to go to a local engineer to replace the filling link and tackle the situation.

How to keep your boiler from breaking down in the future:

Regular boiler service is the best way to avoid costly, inconvenient, and even dangerous boiler faults. In fact, you should have all gas appliances in your home safely checked and serviced on an annual basis by a Gas Safe registered engineer to ensure that your Worcester boiler warranty is valid too.

High pressure can damage your boiler in a variety of ways, including leaks in the system and a build-up that can eventually cause permanent damage. If you notice that your hot water isn’t as warm as it should be, it’s possible that your low boiler pressure is affecting the temperature of your hot water.

Why wait and watch your boiler break down? We provide boiler cover with free annual boiler servicing, so you can rely on us to assist and check your boiler on a regular basis instead of making a yearly appointment.


worcester bosch Which?

Worcester Boiler pressure: Final Words

The full procedure of repressurising a Worcester combi boiler must be done with maximum alert on performing all the steps mentioned above properly, or you could get a Worcester boiler service to get a professional to do it for you.

Here are some of the other main boiler manufacturers that also often require the pressure topping up and we have provided a guide for each of them:

If not you might be a reason for doing any damage to your boiler and this could be costly unless you have a boiler cover plan.

If you would like to get a fixed price on a new boiler we can get you exactly that in just 20 seconds.

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Written by
James Elston
James Elston Director Of Boiler Central
Posted on: 3rd December 2023

James Elston is our resident boiler replacement and heating expert here at Boiler Central. With over 20 years experience in the boiler installation industry, James ensures that he knows everything there is about our Gas Safe boiler installations, energy saving and home heating solutions. This can be from simply procuring the latest best combi boilers, to reviewing and ensuring that Boiler Central maintains the highest standards across our boiler installation company.

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