How to repressurise your Worcester Bosch Boiler - Palace Plumbers

How to repressurise your Worcester Bosch Boiler

All Worcester combination and system boilers need their system pressure to be topped up with cold water from the mains at some point in their lifetime.

If you notice that the pressure gauge on the front of your boiler has dropped into the red zone, it’s an indication that your boiler needs to be re-pressurised.

Boiler Pressure Gauge
Image: Boiler Pressure Gauge

It’s common for this to happen after removing a radiator to decorate, or it might just be the case that your heating system isn’t heating up properly.

How to pressure your boiler with an internal filling key

The internal filling key is a plastic, specially designed tool that is used to unlock, and lock, the unit.

Internal Filling Key
Image: Internal Filling Key

1. Locate the internal filling key

On the underside of your Worcester boiler there should be a white plastic tray. Remove the tray and locate the key.

Remove Boiler Tray
Image:Remove Boiler Tray

2. Locate the arrows on the key

Notice the white arrows pointing upwards near the base of the key. You’ll need these to line up the key in the manifold.

White Arrows on Filling Key
Image: White Arrows on Filling Key

3. Locate the manifold

The manifold is made from black plastic and is linked from your cold mains into the boiler through to your central heating return.

Boiler Manifold
Image:Boiler Manifold

4. Locate the padlock symbols

The padlock symbols are positioned next to one another on the manifold plastic. It’s important that you identify which is which as you’ll need to make sure that your internal filling key is positioned correctly to carry out this procedure.

Manifold Padlock Symbols
Image: Manifold Padlock Symbols

5. Push the key into the manifold

Locate the white arrows on the key and line up with the open padlock symbol position on the plastic of the manifold, push the key up inside the tubing and turn it to the closed padlock symbol position. It’s important to make sure that the key is pushed snugly into the manifold.

Filling Key in Manifold
Image: Filling Key in Manifold

6. Allow water into the system

Now that the internal filling key is in the closed position you need to turn the white plastic nut anticlockwise and you should begin to hear water filling into the heating system.

Turning the Nut
Image: Turning the Nut

7. Monitor the boiler pressure.

Now that water is entering the system you need to keep an eye on the pressure gauge on the front of your boiler. When it reaches the required 1.5 tighten the white plastic nut back up until you can hear the water stop.

Pressure Gauge OK
Image: Pressure Gauge OK

8. Remove the internal filling key

Turn the key back to the lock padlock symbol position. As you remove the key from the manifold you may notice a few drops of water escape. This is fine. If water continues to come out you might want to check that the white nut in the last step is tightened up properly.

Now your boiler is pressurised and the black needle is back into the green area of the pressure gauge.

Problems when re-pressurising your boiler

What if the needle goes up too high into the red section?

Don’t worry. An easy fix is to bleed a little bit of air from your radiators. You might then have to repeat the process as pressure has dropped again.

What happens if the key gets stuck?

Don’t panic. Don’t move it as this could potentially lead to the boiler becoming over pressurised and cause damage to the unit. It might be the case that the filling link needs replacing so its best to call one of our local engineers who can come and assess the situation.

Talk to our team for help and advice or to book

Call 020 3880 5666

Your call may be recorded for training or quality purposes

Important Information regarding Coronavirus (Covid-19)

In the light of the new Government guidance announced by our Prime Minister, we have taken the decision to temporarily close our services with immediate effect.

We have taken this decision in order to protect the wellbeing of you, our customers, and our team.

The circumstances are extremely fluid but in this confusing and difficult time, our priority is to keep you, our customers, safe as the situation develops.

We have not taken this decision lightly but the safety of our people, our customers and the communities in which we serve remains our number one priority.

If you have any questions, please email our customer services team at

We will update our website when this temporarily closure can be lifted again.

Thank you for your support in this challenging time.